Copyright: Copyright (c) 1990-1996 ESRI, Inc.


Error message displayed when a topic is not found
Topic not available

Sorry, the topic you chose to display is not available in ArcView's help system.

To see ArcView's Help Contents, Index, and Find tabs, please click the Help Topics button.


Analysis Properties

The analysis properties allow you to set the output spatial extent and resolution for analysis operations. In the dialog box that appears, you can choose an extent, cell size, and mask for creating output with operations in the Analysis menu.

Available when the active view contains at least one theme.

Since analysis properties are specific to a view, you can work at different extents and scales in different views without having to reset the analysis properties. You merely have to set the analysis properties once for each view.


Analysis Properties Dialog
Analysis Properties (Dialog box)

Displays the properties to be used to create output during analysis. These properties are specific to the active view. You can view and change the following properties

 The spatial extent for output themes.

 The cell size, or resolution, for output grid themes.

 The area within the extent that analysis should take place in.

These properties are only used for operations found in the Analysis menu.

Which of the following dialog box options do you want to know more about?

Analysis Extent

Analysis Cell Size

Number of Rows or Columns

Analysis Mask


Analysis Properties Dialog Cell Size
Analysis Cell Size (Dialog box)

The Analysis Cell Size defines the cell size of the output grid theme. The cell size is the resolution that will be used to create output grid themes. Set the Analysis Cell Size to

 Minimum Of Inputs - Sets cell size according to the smallest cell size of the input grid themes used by an operation.

 Maximum of Inputs - Sets cell size according to the largest cell size of the input grid themes used by an operation.

 As Specified Below - You set the cell size by typing it in.

 Current Value - Resets the cell size to the value set when the dialog was brought up.

 Same As <Grid Theme> - Sets the cell size to the cell size for whichever grid theme in the view you choose.

The cell size to be used for output grid themes will be displayed in the Cell Size type-in box below the Analysis Cell Size dropdown list.


Analysis Properties Dialog Extent
Analysis Extent (Dialog box)

The Analysis Extent defines the spatial extent for output grid themes. A grid theme created by an analysis operation uses the geographic coordinates of the Analysis Extent. Set the Analysis Extent to

 Same As View - Sets extent of output themes to be the same as the view extent.

 Same As Display - Sets extent to the extent of the display at that time. If the extent of the display is changed after the analysis properties are set, the analysis extent will not change.

 Intersection Of Inputs - Sets extent to the area made by the overlap of the input theme extents.

 Union Of Inputs - Sets extent to that of all input theme extents, as if you had drawn a box around all the input themes.

 As Specified Below - You set the extent by typing in geographical coordinates for the top, bottom, left, and right of the extent.

 Current Value - Resets the extent to the value set when the dialog was brought up.

 Same As <Theme> - Sets extent to the extent of whichever theme in the view you choose.

The coordinates that define the Analysis Extent are displayed in the Left, Bottom, Top, or Right type-in boxes, if they are known.


Analysis Properties Dialog Mask
Analysis Mask (Dialog box)

The Analysis Mask defines the area within the extent that analysis will occur. Areas in the mask that have cells with No Data values will also be No Data in the output grid theme of an analysis operation. Set the Analysis Mask to

 No Mask Set - The Spatial Analyst uses the entire extent.

 <Grid Theme> - Sets the mask to whichever grid theme in the view you choose. Cells in the chosen grid theme that are No Data will remain as No Data in any output grid theme.


Analysis Properties Dialog Rows Columns
Number of Rows/Columns (Dialog box)

The Number of Rows and Number of Columns type-in boxes allows you to define the number of rows and columns an output grid theme will be created with.

When you type into either of these type-in boxes, the Analysis Cell Size changes to As Specified Below. You must press the return key on the keyboard after entering a value for Number of Rows or Number of Columns to apply the new value.


Assign Proximity

Assigns areas of proximity to features found in the active theme.

Creates a grid theme as output. Each cell location in the grid theme is allocated to the closest feature, determined by Euclidean distance.

Available when a single grid or feature theme is active.

Works only on the selected set of features. If the active theme doesn't contain a selected set, all features in the active theme are used.

All cells in a grid theme but those with the value of No Data are considered features.


Calculate Density

Calculates a continuous density surface from points.

Creates a grid theme as output. Each cell in that theme will contain the number of occurrences per square unit of an area surrounding a location.

Available when a single point or multipoint theme is active.

Works only on the selected set of points. If the active theme does not contain a selected set, all points in the active theme are used.


Calculate Density Dialog
Calculate Density (Dialog box)

Displays the parameters used to create density from a point theme.

Dialog box options

Population Field   The Field in the active theme that contains the attribute to calculate density with. All numeric fields in the theme are displayed, along with the <None> option. Use <None> if you want each point to have a value of one.

The value of Population Field for a multipoint feature will be used for each point found in it. So a multipoint feature with 3 points and a value of 300 is treated as 3 points, each with a value of 300.

Search Radius   The distance used to search from each cell in the output grid theme for points to be used in the density calculation. The distance is reported in distance units if they’re specified for the view. If distance units aren’t specified for the view, then distance is reported in map units. By default, the radius value is initially set to the smaller distance of the width and height of the extent of the input point theme (or the extent of the selection) divided by 30.

Density Type   The method for calculating density. Density Type can be

 Simple - Density is calculated for each cell by summing the value found in Population Field for each point found in the Search Radius and dividing by the area of the circle in Area Units.

 Kernel - Density is calculated the same way as with Simple, except the value found in Population Field is distributed around each point. The result is a smoother looking output.

Area Units   The units output density values are expressed in. The output density values are occurrences per Area Units. If the map units of the view aren’t set, then the Area Units will be set to Square Map Units and cannot be changed. If the map units of the view are set, Area Units can be Square Miles, Square Kilometers, Acres, Hectares, Square Yards, Square Inches, Square Meters, Square Centimeters, or Square Millimeters.


Cell Statistics

Overlays multiple layers and calculates a statistic using the values at each location.

Creates a grid theme as output. It calculates a statistic for each cell in the output grid theme, based on the values for the same location of multiple input grid themes. You could use it, for instance, to calculate the average crop yields for each cell between 1980 and 1990 in an agricultural community. Summary statistics include majority, maximum, mean, median, minimum, minority, range, standard deviation, sum, and variety.

Available when multiple grid themes are active.


Edit Theme Expression

Brings up the Map Query or Map Calculator dialogs for a grid theme that was created by an expression.

Allows you to redefine your analysis by changing that expression.

Available when one or many grid themes created by the Map Query or Map Calculator dialogs are active.


Find Distance

Finds the distance to the closest feature in the active theme.

Creates a grid theme as output. Each cell in the output grid theme contains the distance from that location to the nearest feature.

Available when a single grid or feature theme is active.

Works only on the selected set of features. If the active theme doesn't contain a selected set, all features in the active theme are used.

All cells in a grid theme but those with the value of No Data are considered features.


Grid Definition Theme Properties
Definition (Theme Properties dialog box)

Shows how the contents of the grid theme are defined.

Dialog box options

Name   The name of the theme. Theme names may include multiple words along with spaces, numbers, and punctuation.

Source   The name of the data source that the theme represents. You can't change the data source for an existing theme.

CellSize   The size of each cell in the theme. Width and height are the same, so only one distance is listed.

Rows   The number of rows in the theme.

Cols   The number of columns in the theme.

Left   The minimum X coordinate of the theme’s extent.

Right   The maximum X coordinate of the theme’s extent.

Bottom   The minimum Y coordinate of the theme’s extent.

Top   The maximum Y coordinate of the theme’s extent.

Type   The data type of the theme. The Type will be either Integer or Float.

Status   The status of the theme’s data source. If the Status is permanent then the data source associated with the theme will remain on disk after the theme is deleted. If the Status is temporary then the data source associated with the theme will be deleted when the theme is deleted. To make a temporary data source permanent, choose Save Data Set in the Theme menu.

Comments   Comments documenting the theme. Lets you leave a note describing what the theme represents, why it was created, and so forth. Comments are stored only with the theme, not the data source.


Histogram

 Creates a histogram chart of the active grid theme.

Each class in the grid theme’s legend makes one bar on the histogram, each bar representing the number of cells with values in that class.

Available when a single grid theme is active.

If selected graphics are present, then only the cells contained in or intersected by the graphics will be used to create the chart.


Histogram By Zone

Creates a chart with a separate histogram distribution of a grid theme for each area of the same attribute (zone) in another theme.

Each histogram distribution is made up of cells contained in or intersected by the features of a zone. Each class in the grid theme’s legend makes one bar on that histogram, where each bar represents the number of cells that have values that fall into that class.

Available when a single feature or integer grid theme is active, and the view contains at least one grid theme.

A separate distribution will be created for each selected zone in the zone theme. If the zone theme doesn't contain a selected set, then a distribution will be created for every zone in the theme.


Legend Editor Advanced Options Grid Themes
Legend Editor Advanced Options for Grid Themes (Dialog box)

Allows you to set a brightness theme for the display of a grid theme. The brightness theme’s cell values will be used to alter the brightness of the colors in a grid theme’s display.

Dialog box options

Brightness Theme   The grid theme to use for the brightness theme. All grid themes found in the view will be listed.

Minimum Cell Brightness   The value that the lowest cell value in the brightness theme will be mapped to. The Minimum Cell Brightness has to be a number between 0 and 100.

Maximum Cell Brightness   The value that the highest cell value in the brightness theme will be mapped to. The Maximum Cell Brightness has to be a number between 0 and 100.

Values in between the lowest and highest cell values of the brightness theme are mapped between the Minimum Cell Brightness and the Maximum Cell Brightness by applying a linear stretch. Giving the Minimum Cell Brightness a higher value than the Maximum Cell Brightness makes lower values brighter than higher values. An example of this would be having locations closer to roads brighter than locations farther away.

Mapping the Minimum or Maximum Cell Brightness to the value of 0 will result in black. 100 will result in white.


Map Calculator

Performs analysis on grid themes using math expressions. Arithmetic, trigonometric, Boolean, and relational operations are available.

Creates a grid theme as output. The output grid theme will remember the expression that created it. You will be able to change the expression and re-evaluate the grid theme without having to create a new grid theme.

Available when the active view contains at least one grid theme.


Map Calculator Dialog
Map Calculator (Dialog box)

Allows you to create mathematical statements with the grid themes found in the active view. Creates an output grid theme using an expression. If you change the expression, it will change the values in the output grid theme instead of creating a new output.

The dialog won’t let you use something that doesn’t make sense at a particular time. When the dialog first comes up, you will only be able to select a grid theme or number. It does not make sense to start an expression with anything else. Once you select a grid theme you won’t be able to select another grid theme or number until you choose an operator. As you build your expression, it will be displayed in the dialog. You are also allowed to type into the expression displayed in the expression box. Once you type into the expression box, the dialog is unable to help you press the correct buttons to build an expression until you use another button in the dialog.

If you would like to apply an operator to just part of the expression, then highlight that part in the expression box and hit the Parenthesis button [image] before using the operator.

Dialog box options

Layers   All of the grid themes in the active view will be shown in the Layers list. Double-click on a Layer to use it in the expression. An integer grid theme will have a separate layer for each field found in its table. These will be denoted as [<Theme name>.<Field name>]. This is useful if you have an integer grid theme of soil types that also has a field of pH values. If you need to use pH in an expression, you can select [Soils.pH].

Numbers   Numbers can be thought of as grid themes that have the same value for every cell. For example, multiplying a grid theme by 3, would be like multiplying the value of each cell by 3. To use a number as a grid theme, press the AsGrid button [image] after you input the number. Numbers used as arguments for other functions or operators, such as rotation angle, don’t need to be modified with AsGrid.

Expression box   Displays the expression being built. Any Avenue expression that results in a grid object can be typed into the expression box.

Operators   The Map Calculator offers many operators that can be used between two grid themes or numbers, like addition [image], or used on a grid theme or number, like a logarithm [image].

Which set of operators would you like more information on?

Arithmetic

Relational

Boolean

Logarithmic

Trigonometric

Powers


Map Calculator Dialog Add
Arithmetic operators (Dialog box)

Arithmetic operators can be found in two different places in the Map Calculator. The four basic arithmetic operators of multiplication, division, subtraction, and addition can be found as buttons to the right of the Layers list. Other miscellaneous arithmetic operators can be found on the right side of the dialog by choosing Arithmetic in the dropdown list at the top right corner of the dialog. Arithmetic operators include

 Multiplication.

 Division.

 Subtraction.

 Addition.

 Returns the absolute value.

 Returns the next highest integer value that is greater than or equal to the input.

 Returns the next lowest integer value that is less than or equal to the input.

 Converts floating point values to integer values by truncating the decimal.

 Converts integer values to floating point values.

 Returns a value of 1 (TRUE) if the cell contains a No Data value, or a value of 0 (FALSE) if it does contain a valid data value.


Map Calculator Dialog Boo
Boolean operators (Dialog box)

The Boolean operators of the Map Calculator are found in the button pad to the right of the number button pad. Boolean operators include

 Returns a value of 1 (TRUE) if both inputs have non zero values, or a value of 0 (FALSE) if not.

 Returns a value of 1 if one input has a non zero value, or a value of 0 if not.

 Returns a value of 1 if one input has a non zero value and the other has a zero value, otherwise a value of 0 is returned.

 Returns a value of 0 for each non zero value, and a value of 1 for each zero value.


Map Calculator Dialog Log
Logarithmic operators (Dialog box)

Logarithmic operators perform logarithm and exponential analysis on grid themes or numbers. Choose Logarithms in the dropdown list at the top right corner of the dialog and the operators will appear in the right side of the dialog. Logarithmic operators include

 The base e exponential.

 The base 2 exponential.

 The base 10 exponential.

 The natural logarithm.

 The base 2 logarithm.

 The base 10 logarithm.


Map Calculator Dialog Pow
Power operators (Dialog box)

Power operators are used to raise grid themes or numbers to certain powers. Choose Powers in the dropdown list at the top right corner of the dialog and the operators will appear in the right side of the dialog. Powers operators include

 Takes the square root.

 Raises to the power of 2.

 Raises to the power specified. The power of 2 is used initially. You can change this by typing over the 2 in the expression box.


Map Calculator Dialog Rel
Relational operators (Dialog box)

Relational operators are used to compare the values of two grid themes or numbers on a cell by cell basis. These operators are found in the button pad to the right of the number button pad. Relational operators include

 Returns the value of 1 (TRUE) if two values are equal, or a value of 0 (FALSE) if they’re not.

 Returns the value of 1 if one value is greater than another, or a value of 0 if it’s not.

 Returns the value of 1 if one value is less than another, or a value of 0 if it’s not.

 Returns the value of 1 if two values are not equal, or a value of 0 if they are.

 Returns the value of 1 if one value is greater than or equal to another, or a value of 0 if it’s not.

 Returns the value of 1 if one value is less than or equal to another, or a value of 0 if it’s not.


Map Calculator Dialog Trig
Trigonometric operators (Dialog box)

Trigonometric operators are used to perform trigonometric analysis on a grid theme or number. Input values should be in radians. Choose Trigonometry in the dropdown list at the top right corner of the dialog and the operators will appear in the right side of the dialog. Trigonometric operators include

 Sine.

 Cosine.

 Tangent.

 Inverse sine.

 Inverse cosine.

 Inverse tangent.


Map Query

Allows you to perform a Boolean query on several grid themes.

Creates a grid theme as output. You can change the expression and re-evaluate the grid theme without creating a new grid theme.

Available when the active view contains at least one grid theme.


Map Query Dialog
Map Query (Dialog box)

The Map Query dialog allows you to select areas spatially by defining a Boolean query based on the values of one or more grid themes. The output will be a grid theme with areas that match the query given a value of 1 (TRUE) and areas that do not match the query given a value of 0 (FALSE). If you change the query it will change the values in the output grid theme.

The dialog won't let you use something that doesn’t make sense at a particular time. You can also type into the expression displayed in the expression box of the dialog. Once you do, the dialog is unable to help lead you through the building of an expression until you use another button or selection in the dialog.

Dialog box options

Layers   All of the grid themes in the active view will be shown in the Layers list. Double-click on a Layer to use it in the query. An integer grid theme will have a separate layer for each field found in its table. These will be denoted as [<Theme name>.<Field name>]. This is useful if you have an integer grid theme of soil types that also has a field of pH values. If you need to use pH in an expression you can select [Soils.pH].

Operators   Use these operators to specify relationships between Layers and Values in a query. Click an operator to place it into the expression box.

 - equals

 - greater than

 - less than

 - not equal to

 - greater than or equal to

 - less than or equal to

 expressions enclosed in parentheses are evaluated first

 - both expressions are true, such as, [elevation] >= 100 and [slope] <= 20

 - at least one expression is true, such as, [rainfall] < 20 or [soils.ph] > 3

 - excludes, such as, not ( [states] = "california" )

To enclose an expression in parentheses, select it in the expression box by dragging over it with the mouse and then clicking the [image] operator. Parentheses will enclose the selected part of the query.

Values   Lists the values for the chosen Layer. If the chosen Layer is from an integer grid theme, the Unique Values found in this Layer will be displayed. If it’s from a floating point grid theme, then the list will be Sample Values from the range of values found in the theme. Double-click a value to place it into the expression box. If the value you want to use is not in the list, type it into the expression box.

Update Values   By default, the Values list updates each time you choose a Layer. If there are a lot of values, it may take a moment for the values to be updated. Click this choice off if you don't want to update the values. This is particularly helpful if your query compares one Layer to another and you don't need to see their values, or if you want to type specific values into the expression box instead of choosing them from the Values list.

Expression box   This is where your query is displayed as you build it.


Neighborhood Statistics

Calculates a statistic for the values found in a specified neighborhood using a point or grid theme.

Creates a grid theme as output. The output theme will contain the desired statistic value for the neighborhood defined around each cell. Statistics include majority, maximum, mean, median, minimum, minority, range, standard deviation, sum, and variety. Neighborhood shapes include rectangle, circle, wedge, and doughnut.

Available when a single grid, point, or multipoint theme is active.

If the input is a point theme, only the selected set of points are used. If the point theme doesn't contain a selected set, all points are used.


Neighborhood Statistics Dialog
Neighborhood Statistics (Dialog box)

Analyzes the points of a point theme or cells of a grid theme with the statistics type and neighborhood you enter. All points or cells that fall within the neighborhood will be used in the calculation.

Dialog box options

Field   Defines the values each point in a theme will have. Only used when the input theme is a point theme. Only numeric fields in the point theme are shown.

The value of Field for a multipoint feature will be used for each point found in it. So a multipoint feature with 3 points and a value of 300 is treated as 3 points, each with a value of 300.

Statistic   Type of summary statistics that you want calculated for the neighborhood. Statistics can be minimum, maximum, mean, median, sum, range, standard deviation, majority, minority, and variety.

Neighborhood   Shape of the neighborhood you want to use to select points or cells to use to calculate each output cell. The cell center has to be inside the neighborhood for the cell to be considered as part of the neighborhood. Neighborhood can be

 Rectangle - defined by a Width and a Height.

 Circle - defined by a Radius.

 Dough Nut - defined by an Inner Radius and an Outer Radius.

 Wedge - defined by a Radius, a Start Angle expressed in degrees, and an End Angle expressed in degrees.

Units   Units that all distances defining the Neighborhood are expressed in. Units can be

 Map - Units are expressed in the distance units defined for the view. If the distance units are not defined, then the map units of the view will be used.

 Cell - Units are expressed in number of cells. The cell size for the output grid theme is used.


Reclassify

Allows you to change the values in a grid theme by specifying new ones.

Creates an output integer grid theme. Values of No Data can be used as both input and output. Functions to apply standard classifications are available.

Available when a single grid theme is active.


Reclassify Classifications Dialog
Classification (Dialog box)

Allows you to set standard classification methods and the parameters for that classification.

Dialog box options

Type   Classification method to reclassify the data with. Type can be

 Equal Area - Reclassifies so there is an equal number of cells in each of the output classes.

 Equal Interval - Divides the range of cell values into equal sized sub-ranges.

 Natural Breaks - Identifies breakpoints between classes using a statistical formula (Jenk’s optimization). The Jenk’s method minimizes the sum of the variance within each of the classes. Natural Breaks finds groupings and patterns inherent in your data.

 Quantile - Reclassifies so there is an equal number of features in each of the output classes. For a grid theme this is exactly the same as Equal Area.

 Standard Deviation - Finds the mean cell value and then places class breaks above and below the mean at intervals of either 1/4, 1/2, or 1 standard deviations until all the cell values are contained within the classes. Any cell values that are beyond three standard deviations from the mean are put into two classes, greater than three standard deviations above the mean ("> 3 Std Dev.") and less than three standard deviations below the mean ("< -3 Std. Dev.").

Only the Equal Interval and Standard Deviation methods are available for floating point grid themes.

Number of classes   Shows the number of classifications that will be generated when you classify the values in the Classification Field. This is not used for the Standard Deviation classification.

Round values at   Shows the rounding scheme that will be used to determine where class breaks are placed.

Break Classes At   This option is shown for Standard Deviation classification instead of Round values at. Sets class breaks at 1, ½, or ¼ standard deviations.


Reclassify Dialog
Reclassify Values (Dialog box)

Allows you to reclassify a value, a range of values, or a list of values of a grid theme to another value in a new grid theme.

Dialog box options

Classification Field   The field in the input grid theme's table that will be used to supply the Old Values. If the grid theme does not have a table, like floating point grid themes, the only field shown is Value.

Classify   Presents to you the Classification dialog for filling out the parameters to classify the Old Values.

Unique   Sets the Old Values to the unique values found in the Classification Field. Only available for integer grid themes.

Lookup   Sets the New Value to a value found in a field in the input grid theme's table. In the Lookup Values dialog you can pick the field to use as the New Value. Only available for integer grid themes.

Old Values   The range, list, or single value to be changed to the New Value. Any combination of ranges, lists, or single values can be used. Separate ranges with a dash (-),lists with a comma (,). To edit an entry click on it and type in the new specification.

New Value   The new value can be either a single value or "No Data".

   Adds a new record to the reclassification, below the selected record. Select a record by clicking on the column to the left of the Old Values column.

   Deletes the selected record in the reclassification. Select a record by clicking on the column to the left of the Old Values column.

Load   Enables you to load a previously saved reclassification from a file (.avc). In the Load Classification dialog, you may navigate to the reclassification file you wish to load.

Save   Saves your reclassification to a file (.avc). In the Save Classification dialog, you may navigate to where you would like to save your reclassification file.


Reclassify Lookup Dialog
Lookup Values (Dialog box)

Sets the values in New Value to the values found in the selected field.

Dialog box options

Field   Shows all the fields in the table of the input grid theme except the field selected as the Classification Field.


Summarize Zones

Computes a summary statistic for each zone in a grid or feature theme (the zone theme) based on the cell values in another grid theme (the value theme) that fall within each zone. A zone consists of the set of features or cells in the zone theme that have the same attribute value.

Creates an output table and chart. The output table will contain all of the summary statistics computed for each zone. The output chart will display one of the statistics found in the table. Summary statistics for an integer value theme include area, minimum, maximum, range, mean, standard deviation, sum, variety, majority, minority, and median. Summary statistics for a floating point value theme include area, minimum, maximum, range, mean, standard deviation, and sum.

Available when a single feature or integer grid theme is active and the view contains at least one grid theme.

Works only on the selected set of features. If the active theme doesn't contain a selected set, all features in the active theme are used.


Tabulate Areas

Performs a cross tabulation of the zones between two input themes. For example, summarizing the area of each land use type within each county.

Creates an output table. The zones in one theme create the rows of the resulting table and the zones in another theme produce the columns. The values in the resulting table identify the area of each zone in one theme encompassed within each zone in another theme.

Available when the view contains at least two feature or two integer grid themes, or one of each.

Works only on the selected set of features. If neither theme contains a selected set, all features in that theme are used.


Tabulate Areas Dialog
Tabulate Areas (Dialog box)

Performs a cross tabulation of the zones between two input themes. The zones in the Row Theme create the rows of the resulting table and the zones in the Column Theme produce the columns. The values in the resulting table identify the area of each zone in the Column Theme encompassed within each zone in the Row Theme. You can use it, for example, to summarize the area of each land use type within each county.

Point, line, polygon, and grid themes can be used. If you use a point or line theme, then the area intersected by those features will be reported.

A zone consists of the set of features or cells in a theme that have the same attribute value.

Dialog box options

Row Theme   Theme that defines the rows in the output table. There will be a record for each unique zone in the Row Theme. Each record contains the area of each zone in the Column Theme within that zone. The Row Theme can be a point, line, polygon, or grid theme.

Row Field   Field used to define zones in the row theme.

Column Theme   Theme that defines the columns in the output table. There will be a field for each unique zone in the Column Theme. Each field will hold the area for that zone within the zones of the Row Theme.

Column Field   Field used to define the zones in the column theme.


Calculating cell statistics across multiple grid themes
To calculate cell statistics across multiple grid themes

1	Activate multiple grid themes on which to calculate statistics.

2	From the Analysis menu, choose Cell Statistics.

3	From the dropdown list, choose the statistic to apply. Press OK.

For each cell location in the analysis extent, a statistic is calculated based on the values for the locations between the input grid themes. The statistics available are Majority, Maximum, Mean, Median, Minimum, Minority, Range, Standard Deviation, Sum, and # of Unique Values.

The output grid theme from Cell Statistics is automatically named for the statistics used to create it. The grid data set associated with the output theme is written to the project's working directory, with the name being the abbreviation of the statistic that created it followed by a unique number. Use Properties in the Theme menu to find out which data set is associated with which theme. Use Properties in the Project menu to change the project's working directory. The grid data set associated with the output theme is temporary and will be deleted when the theme is deleted. Use Save Data Set in the Theme menu or save the project to prevent the grid data set from being deleted when the theme is deleted.


Calculating density from point estimates of a population
To calculate density from point estimates of a population

1	Activate a point or multipoint theme.

2	From the Analysis menu, choose Calculate Density.

3	If the view's analysis properties haven't been set to a specific value, then you'll be prompted to set the extent and cell size for the output grid theme. Do so in the Output Grid Specification dialog and press OK. For more information on setting the analysis extent and cell size using this dialog, see Output Grid Specification (Dialog box).

4	In the Calculate Density dialog, choose a field from the Population Field dropdown list to identify the measured quantity to distribute through the output grid theme. A choice of <None> assigns a value of 1 to all points in the input point theme. The value of Population Field for a multipoint feature will be used for each point in that feature.

5	Specify a search radius in the Search Radius type-in box. The radius determines the distance to search for points from each cell in the output grid theme. The radius is reported in the distance units specified for the view. If the view's distance units are not set, then the search radius is reported in map units. By default, the radius value is initially set to the smaller distance of the width and height of the extent of the input point theme (or the extent of the selection) divided by 30.

6	Choose either Simple or Kernel in the Density Type dropdown list.

7	Choose the units that you want the density values to be presented in from the Area Units dropdown list. Press OK.

Calculate Density distributes the measured quantity of an input point theme throughout a landscape to produce a continuous surface.

The two types of density methods are

 Simple - Density is calculated for each cell by summing the value found in Population Field for each point found in the Search Radius and dividing by the area of the circle in Area Units.

 Kernel - Density is calculated the same way as with the Simple method except the value found in Population Field is distributed out from each point. The result is a smoother looking output.

The output density values will be the occurrences of the measured quantity per specified Area Unit. If the map units of the view are not set, then the Area Units are set to Square Map Units and cannot be changed. If the map units of the view are set, Area Units can be Square Miles, Square Kilometers, Acres, Hectares, Square Yards, Square Inches, Square Meters, Square Centimeters, or Square Millimeters.

Calculate Density works off of the selected set of the active theme. If the active theme does not have a selected set, then all points in theme are used. For more information on selecting features, see Selecting features on a view.

The output grid theme from Calculate Density is automatically named "Density from" followed by the name of the input theme. The grid data set associated with the output theme is written to the project's working directory, with the name "denst" followed by a unique number. Use Properties in the Theme menu to find out which data set is associated with which theme. Use Properties in the Project menu to change the project's working directory. The grid data set associated with the output theme is temporary and will be deleted when the theme is deleted. Use Save Data Set in the Theme menu or save the project to prevent the grid data set from being deleted when the theme is deleted.


Calculating distance surfaces and buffers

To analyze distance with the Spatial Analyst, start by using Find Distance in the Analysis menu to create a grid theme containing the distance to the nearest feature for each cell. Features used to find distance can be points, lines, polygons, or non-null cells. Euclidean distance is calculated between each of the output cells that doesn't contain a feature, to the closest feature. Output cells that contain features are given a value of zero. Use this continuous distance grid theme to create discrete distance buffers or find features within certain distances of other features.

Find Distance works off of the selected set of the active theme. If the active theme does not have a selected set, then all its features will be used. If you wanted to create a continuous surface of distance from residential areas in a land use theme, you would first select all residential areas in the theme with the Query builder [image]. For more information on selecting features, see Selecting features on a view.

Every cell that has a value (including 0) is seen as a feature for a grid theme. If a grid theme is used as input to Find Distance, a distance will be calculated for every cell in the active theme that has a value of No Data. If you want to create a continuous surface of distance from roads in a grid theme which has the value of 1 for roads and 0 for areas without a road, you first select all cells with a value of 1. For more information on how to select cells in a grid theme, see Show me all cells that have a specified attribute.

The output grid theme from Find Distance is automatically named "Distance to" followed by the name of the input theme. The grid data set associated with the output theme is written to the project's working directory, with the name "dist" followed by a unique number. Use Properties in the Theme menu to find out which data set is associated with which theme. Use Properties in the Project menu to change the project's working directory. The grid data set associated with the output theme is temporary and will be deleted when the theme is deleted. Use Save Data Set in the Theme menu or save the project to prevent the grid data set from being deleted when the theme is deleted.

How do you want to use distance?

Generate a continuous surface of distance from source features

Find a single discrete distance buffer from source features

Create a set of discrete distance buffers from source features

Find features with locations more than a certain distance from their closest feature in another theme


Calculating neighborhood statistics
To calculate neighborhood statistics

For a grid theme

1	Activate a grid theme.

2	From the Analysis menu, choose Neighborhood Statistics.

3	From the Statistics dropdown list, choose a statistic. The available statistics are Minimum, Maximum, Mean, Median, Sum, Range, Standard Deviation, Majority, Minority, and Variety.

4	Choose the neighborhood from the Neighborhood dropdown list. The available neighborhoods are Rectangle, Circle, Dough Nut, and Wedge.

5	When you choose a neighborhood from the Neighborhood dropdown list the available type-in boxes for that neighborhood appear. Specify the parameters for the chosen neighborhood. With Rectangle, enter the width and height of the rectangle. With Circle, enter the radius of the circle. With Dough Nut, enter the inner radius of the dough nut (cells not to include in the neighborhood) and the outer radius. With Wedge, enter the radius of the wedge, and the start and end compass degree specifications to define the wedge.

6	In Units, specify whether the units for the neighborhood parameters will be in map or cell units.

For a point or multipoint theme

1	Activate a point or multipoint theme.

2	From the Analysis menu, choose Neighborhood Statistics.

3	If the view's analysis properties haven't been set to a specific value, then you'll be prompted to set the extent and cell size for the output grid theme. Do so in the Output Grid Specification dialog and press OK. For more information on setting the analysis extent and cell size using this dialog, see Output Grid Specification (Dialog box).

4	Choose a field that defines the values each point in a theme will have. The value of Field for a multipoint feature will be used for each point found in that feature.

5	From the Statistics dropdown list, choose a statistic. The available statistics are Minimum, Maximum, Mean, Median, Sum, Range, Standard Deviation, Majority, Minority, and Variety.

6	Choose the neighborhood from the Neighborhood dropdown list. The available neighborhoods are Rectangle, Circle, Dough Nut, and Wedge.

7	When you choose a neighborhood from the Neighborhood dropdown list the available type-in boxes for that neighborhood appear. Specify the parameters for the chosen neighborhood. With Rectangle, enter the width and height of the rectangle. With Circle, enter the radius of the circle. With Dough Nut, enter the inner radius of the dough nut (cells not to include in the neighborhood) and the outer radius. With Wedge, enter the radius of the wedge, and the start and end compass degree specifications to define the wedge.

8	In Units, specify whether the units for the neighborhood parameters will be in map or cell units.

For each cell in an output grid theme, Neighborhood Statistics computes a statistic based on the values of the cells or points within a specified neighborhood. The larger the neighborhood the longer the processing time.

Neighborhood Statistics works off of the selected set of the active theme if it is a point or multipoint theme. If the active theme does not have a selected set, then all points in the theme are used. For more information on selecting features, see Selecting features on a view.

The output grid theme from Neighborhood Statistics is automatically named "Nbr<stat> of" followed by the name of the input theme, <stat> being the statistics used to create it. The grid data set associated with the output theme is written to the project's working directory, with the name "nb<abbreviated stat>" followed by a unique number. Use Properties in the Theme menu to find out which data set is associated with which theme. Use Properties in the Project menu to change the project's working directory. The grid data set associated with the output theme is temporary and will be deleted when the theme is deleted. Use Save Data Set in the Theme menu or save the project to prevent the grid data set from being deleted when the theme is deleted.


Calculating summary attributes for features using a grid theme
To calculate summary attributes for features using a grid theme

1	Activate a zone theme (an integer grid or feature theme) on which to summarize the zones.

2	From the Analysis menu, choose Summarize Zones.

3	In the Summarize Zones dialog, choose the field defining the zones in the input zone theme from the dropdown list. Press OK.

4	From the dropdown list, choose the value grid theme defining the cell values to summarize within each zone defined by the zone theme. Press OK.

5	Choose a statistic to chart from the dropdown list. With an integer value grid theme the choices are area, minimum, maximum, range, mean, standard deviation, sum, variety, majority, minority, and median. With a floating point value grid theme the choices are area, minimum, maximum, range, mean, standard deviation, and sum. Press OK.

Summarize Zones computes a chart and a table. The output values are a function of the value of the cells in an input value grid theme found within each zone in the zone theme. The values in the input value grid theme can represent, among others, endangered species, vaccinations, housing prices, and sales. Examples of cartographic zones can be parcels in a city, land use categories, forest types, or buffer zones.

The zone theme must be either an integer grid theme or a feature theme. The value theme must be a grid theme, but can be either integer or floating point.

Summarize Zones works off of the selected set of the active theme. If the active theme does not have a selected set, then all features in the theme will be used. For more information on selecting features, see Selecting features on a view.

Every cell that has a value (including 0) is seen as a feature for a grid theme. For more information on how to select cells in a grid theme, see Show me all cells that have a specified attribute.

In the output table, the number of rows is equal to the number of zones defined in the input zone theme; each row value represents the corresponding zone. The columns in the output table are: the number of cells of the input value theme within each zone of input zone theme, the area of the input value grid theme contained within each zone of the input zone theme, and columns that contain statistics of the values of the input value grid theme within each zone of the input zone theme. With an integer value grid theme the statistics are area, minimum, maximum, range, mean, standard deviation, sum, variety, majority, minority, and median. With a floating point value grid theme the statistics are area, minimum, maximum, range, mean, standard deviation, and sum.

The output table can be joined to the table of the input zone theme. Once the output table is joined, its fields can be used to symbolize the input zone theme. You could symbolize tract polygons with the mean distance to the nearest police station. For more information on joining tables, see Joining tables.

The resulting chart is a histogram of the chosen statistic. The x axis has a bar representing each zone of the input zone theme. The bar is the value of the statistic for each zone.

The output table from Summarize Zones is associated with a dBASE file written into the project's working directory. Use Properties in the Project menu to change the project's working directory. The name of the dBASE file will be "zstatX.dbf", with X denoting a unique number.


Create a set of discrete distance buffers
To create a set of discrete distance buffers from source features

1	Click on a theme to make it active.

2	From the Analysis menu, choose Find Distance.

3	If the active theme isn't a grid theme, and the view's analysis properties haven't been set to a specific value, then you'll be prompted to set the extent and cell size for the output grid theme. Do so in the Output Grid Specification dialog and press OK. For more information on setting the analysis extent and cell size using this dialog, see Output Grid Specification (Dialog box).

4	Click on the distance grid theme created by Find Distance to make it active.

5	From the Analysis menu, choose Reclassify.

6	Define the minimum and maximum distance value for each buffer. Either type the ranges in the dialog or use one of the standard classification methods found under the Classify button. After you define the ranges for the buffers, press OK in the Reclassify dialog. For more information on reclassifying data in a grid theme, see Reclassifying the cell values of a grid theme.


Cross tabulating areas
To cross tabulate areas

1	From the Analysis menu, choose Tabulate Areas.

2	Choose the row theme (input theme 1) for the cross tabulation from the Row Theme dropdown list.

3	From the Row Field dropdown list, choose the field defining the zones to use in the cross tabulation.

4	Choose the column theme (input theme 2) for the cross tabulation from the Column Theme dropdown list.

5	From the Column Field dropdown list, choose the field defining the values to use in the cross tabulation. Press OK.

Tabulate Areas performs a cross tabulation of the zones between two input themes. The zones in the first theme create the rows of the resulting table, and the zones in the second theme produce the columns. The values in the resulting table identify the area of each zone of input theme 2 (the column theme) encompassed within each zone in input theme 1 (the row theme).

The input themes to tabulate areas can be either grid or feature themes. The input grid themes must be of integer type. The number of rows in the output table is equal to the number of zones in the input row theme; each value in the Value field represents the corresponding zone in the input row theme. The number of columns in the output grid theme is equal to the number of values in the input column theme; each column represents each value in the input column theme.

Tabulate Areas works off of the selected set of the active theme. If the active theme does not have a selected set, then all features in the theme are used. For more information on selecting features, see Selecting features on a view.

Every cell that has a value (including 0) is seen as a feature for a grid theme. For more information on how to select cells in a grid theme, see Show me all cells that have a specified attribute.

The output table from Tabulate Areas is associated with a dBASE file written into the project's working directory. Use Properties in the Project menu to change the project's working directory. The name of the dBASE file will be "tareaX.dbf", with X denoting a unique number.


C API for grid data set IO
C API for grid data set I/O

The Spatial Analyst includes a C programming API (Application Programming Interface). This API is a grid data set I/O (input/output) library that allows you to read and write ESRI grid data sets directly. With it, you can attach custom raster modeling or analysis programs to the Spatial Analyst or perform data conversion for formats not supported with the Spatial Analyst. The library is meant to be used with the Spatial Analyst only.

You can find the library in the gridio directory under the ArcView installation directory. In this directory you will also find licensing information, code samples, a header file, and documentation on how to use the library.


Define the area of space allocated
To define the area of space allocated to each feature

1	Click on a theme to make it active.

2	From the Analysis menu, choose Assign Proximity.

3	If the active theme isn't a grid theme, and the view's analysis properties haven't been set to a specific value, then you'll be prompted to set the extent and cell size for the output grid theme. Do so in the Output Grid Specification dialog and press OK. For more information on setting the analysis extent and cell size using this dialog, see Output Grid Specification (Dialog box).

4	If the active theme is a feature theme choose a field to give values to the cells in the output grid theme. Press OK. You now have a proximity grid theme.


Determining proximity

To do proximity analysis with the Spatial Analyst you start by using Assign Proximity in the Analysis menu to create a grid theme that stores for each cell the id, or value, of the nearest feature. The features used to assign proximity can be points, lines, polygons, or non-null cells. Each cell in the output grid theme is given the value found in a specified field for each feature. This proximity theme can be used to define the space allocated to each feature or to identify the closest feature in another theme.

Assign Proximity works off of the selected set of the active theme. If the active theme has no selected set, then all features in the theme are used. If you wanted to create proximity areas for residential and commercial classes in a land use theme, you would first select all residential and commercial areas in the theme with the Query builder [image]. For more information on selecting features, see Selecting features on a view.

Every cell that has a value (including 0) is seen as a feature for a grid theme. If you use a grid theme as input for Assign Proximity, proximity will be calculated for every cell in the active theme that has a value of No Data. If you want to create proximity areas for roads in a grid theme with speed limit as the value for the roads and 0 for areas that don't contain a road, you first select all cells with a value greater than 0. For more information on how to select cells in a grid theme, see Show me all cells that have a specified attribute.

The output grid theme from Assign Proximity is automatically named "Proximity to" followed by the name of the input theme. The grid data set associated with the output theme is written to the project's working directory, with the name "prox" followed by a unique number. Use Properties in the Theme menu to find out which data set is associated with which theme. Use Properties in the Project menu to change the project's working directory. The grid data set associated with the output theme is temporary and will be deleted when the theme is deleted. Use Save Data Set in the Theme menu or save the project to prevent the grid data set from being deleted when the theme is deleted.

What type of proximity analysis would you like to perform?

Find the closest feature in another theme

Define the area of space allocated to each feature


Displaying a histogram of cell values

A histogram is an alternative way of displaying the data found in a grid theme. It allows you to compare the number of cells with different values in your grid theme as a chart. If your grid theme represents a continuous variable, you can also use the histogram to check if your values are normally distributed or if they have some sort of skew. You are able to chart: all cell values, cell values that intersect with graphic shapes on the display, or cell values that intersect with features in another theme. Charts are created using the classes and symbols of a grid theme's legend. Each bar in the chart represents the number of cells in the grid theme that have the values included in that class. You can change how cell values are grouped by changing the classification of the grid theme's legend.

Which cells do you want to chart in the histogram?

All cells in a grid theme

Cells that intersect a specified shape

Cells that intersect the features in another theme


Find a single discrete distance buffer
To find a single discrete distance buffer from source features

1	Click on a theme to make it active.

2	From the Analysis menu, choose Find Distance.

3	If the active theme isn't a grid theme, and the view's analysis properties haven't been set to a specific value, then you'll be prompted to set the extent and cell size for the output grid theme. Do so in the Output Grid Specification dialog and press OK. For more information on setting the analysis extent and cell size using this dialog, see Output Grid Specification (Dialog box).

4	From the Analysis menu, choose Map Query.

5	In the Map Query dialog, use the newly created distance grid theme to define the range for the buffer you want to create, and press Evaluate. For more information on using the Map Query dialog, see Querying across multiple grid themes.

The result will be a grid theme with values of 1 and 0. Cells with a value of 1 are inside the distance buffer you defined and cells with a value of 0 are outside.

If you want a buffer of all areas less than a certain distance away from features, first double-click on the distance grid theme from the list of Layers in the dialog. Then click on the Less Than button [image], and then double-click on a distance from the list of Values or type the distance in the expression box.

If you want a buffer of all areas greater than a certain distance away from features, first double-click on the distance grid theme from the list of Layers in the dialog. Then click on the Greater Than button [image], and then double-click on a distance from the list of Values or type the distance in the expression box.

If you want a buffer of all areas between two distances away from features, first double-click on the distance grid theme from the list of Layers in the dialog. Then click on the Less Than button [image], and then double-click on a distance from the list of Values or type the distance in the expression box that defines the upper bound of the range of distances desired. To define the lower bound, click on the And button [image], double-click on the distance grid theme from the list of Layers, click on the Greater Than button [image], and then double-click on a distance from the list of Values or type the distance in the expression box that defines the lower bound of the range of distances desired.


Find features more than a certain distance away from points
To find features with locations more than a certain distance from their closest feature in another theme

1	Choose two themes - for each feature in one, you want to find if that feature is more than a certain distance from the closest feature in the other one.

2	Click on the second theme to make it active.

3	From the Analysis menu, choose Find Distance.

4	If the active theme isn't a grid theme, and the view's analysis properties haven't been set to a specific value, then you'll be prompted to set the extent and cell size for the output grid theme. Do so in the Output Grid Specification dialog and press OK. For more information on setting the analysis extent and cell size using this dialog, see Output Grid Specification (Dialog box).

5	Click on the first theme to make it active.

6	From the Analysis menu, choose Summarize Zones.

7	If you want to group the features in the active theme, then choose a field that defines the group as the zone field, and press OK. If you don’t want to group the features, then choose a field that has a unique value for each feature.

8	Choose the distance grid theme created after step 4 as the theme you want to summarize, and press OK.

9	Press Cancel when prompted for a statistic to chart. You're only interested in the table produced from Summarize Zones.

10	Using the field specified with step 7, join the table created with Summarize Zones to the table of the first theme. For more information on joining tables, see Joining tables.

11	Activate the table of the first theme.

12	Press the Query Builder button [image] to bring up the Query Builder.

13	Double-click on the DistX_max field. This field contains the maximum distance that any part of features of the first theme are from the closest feature of the second theme.

14	Click on the Greater Than button [image], and then double-click or type the distance for which you want to find features that contain locations that are farther than that distance. Press the New Set button. If any part of a feature in the first theme is farther than the specified distance from the closest feature in the second theme, then they are highlighted in the view.


Find the closest feature
To find the closest feature in another theme

1	Choose two themes - for each feature in one, you want to find the closest feature in the other one.

2	Click on the second theme to make it active.

3	From the Analysis menu, choose Assign Proximity.

4	If the active theme isn't a grid theme, and the view's analysis properties haven't been set to a specific value, then you'll be prompted to set the extent and cell size for the output grid theme. Do so in the Output Grid Specification dialog and press OK. For more information on setting the analysis extent and cell size using this dialog, see Output Grid Specification (Dialog box).

5	If the active theme is a feature theme choose a field to give values to the cells in the output grid theme. Press OK. You now have a proximity grid theme.

6	Click on the first theme to make it active.

7	From the Analysis menu, choose Summarize Zones.

8	If you want to group the features in the active theme, then choose a field that defines the group as the zone field, and press OK. If you don’t want to group the features, then choose a field that has a unique value for each feature.

9	Choose the proximity grid theme created after step 5 as the theme to summarize, and press OK.

10	Press Cancel when prompted for a statistic to chart. You're only interested in the table produced from Summarize Zones.

11	Using the field specified with step 8, join the table created with Summarize Zones to the table of the first theme. For more information on joining tables, see Joining tables.

The field ProxX_majority shows which feature in theme two each feature in theme one is closest to. If the features of theme one are lines, polygons, or grid cells, then the field shows the feature in theme two that's closest to the majority of the locations for each feature in theme one. This field can be used as the values field for a unique values legend, which shows the distribution of each feature to the closest feature in another theme.

If the field used in step 5 is a string field, then the string values can be added to the table by joining the table of the proximity grid theme created with the first 5 steps with the table of the first theme. Join the Value field in the proximity grid theme to the ProxX_majority field. Then use the field S_Value in place of the ProxX_majority field to define which feature in theme two each feature in theme one is closest to.


Generate a continuous surface of distance
To generate a continuous surface of distance from source features

1	Click on a theme to make it active.

2	From the Analysis menu, choose Find Distance.

3	If the active theme isn't a grid theme, and the view's analysis properties haven't been set to a specific value, then you'll be prompted to set the extent and cell size for the output grid theme. Do so in the Output Grid Specification dialog and press OK. For more information on setting the analysis extent and cell size using this dialog, see Output Grid Specification (Dialog box).


Histogram of all cells
To chart a histogram of all cells in a grid theme

1	Click on a grid theme to make it active.

2	Press the Histogram button [image].

If there are any graphics present in the view, make sure that none of them are selected.


Histogram of cells that intersect a specified shape
To chart a histogram of cells that intersect a specified shape

1	Create a shape with the Draw tool [image]. If you already have a shape, make sure it's selected.

2	Click on a grid theme to make it active.

3	Press the Histogram button [image].

Only cells contained within selected polygon shapes, intersected by selected line shapes, and containing selected point shapes, are used to create the histogram.


Histogram of cells that intersect features
To chart a histogram of cells that intersect features in another theme

1	Click on the theme that contains the features of the areas you want to see a histogram for. Only the selected features in this theme are used to define which cells are used to create the histogram. If the theme does not contain any selected features, then all features are used.

2	From the Analysis menu, choose Histogram By Zone.

3	Choose the field that defines how the features that define the cells to be used are grouped. Press OK. There will be a separate section on the histogram for each unique value found in this field.

4	Choose the grid theme containing the cell values you want to see a histogram for. Press OK.

The points, lines, or polygons in the active theme are used to define what cells are used to create the histogram. Only cells contained within polygon features, intersected by line features, or that contain point features, are used to create the histogram. These features not only define the area, but an attribute of the features defines how the data is grouped on the histogram, a separate group for each unique attribute. This allows you to examine the number of cell values for each class in a grid theme in a localized area defined with another theme. For example, you could examine the number of cells of each land use type that intersect roads that have a 45 or 65 mph speed limit. This allows you to compare the land use types that 45 and 65 mph roads intersect on the same histogram.

An integer grid theme can also be used to define the areas you want to see a histogram for. All cells with the same value are considered a zone. You will get a separate histogram distribution for the cells in one theme that overlay with the cells of each zone in the active grid theme. Only the selected cells of the active grid theme are used to define zones for the histogram. If the active grid theme does not contain any selected cells, then all the cells are used to define zones.


Loading the Spatial Analyst
To load the Spatial Analyst

1	Activate the ArcView Project window.

2	From the File menu, choose Extensions. This will bring up the Extensions dialog.

3	Check the box next to Spatial Analyst in the Extensions dialog. If you want the Spatial Analyst extension to load automatically every time you start ArcView, press the Make Default button after checking the Spatial Analyst. The next time you start ArcView the Spatial Analyst will automatically load.

4	Press OK in the Extensions dialog.


Querying across multiple grid themes
To query across multiple grid themes

1	From the Analysis menu, choose Map Query.

2	The Map Query dialog aids in the creation of an expression that subsets cells that meet the specified criterion of a query. The criterion can be based on single or multiple grid themes. To aid in the creation of the expression, there are three groups of inputs in the Map Query dialog. The first is the Layers scrolling list which identifies the available grid layers in the active view, the second, a series of operators to be used in the evaluation of the expression, and the third, a scrolling list of the Unique or Sample Values within the highlighted layer of the Layers scrolling list. A typical sample session follows.

3	Double-click on a layer from the Layers scrolling list.

4	Press one of the relational operators (e.g., =, <>, >, >=, <, or <=).

5	Double-click on a value from the Sample or Unique Values scrolling list, or type a value into the expression box.

6	Press a Boolean operator (e.g., and or or) from the operator group of buttons.

7	Choose a second layer from the Layers scrolling list.

8	Press a relational operator button.

9	Choose a value from the Sample or Unique Value scrolling list, or type a value into the expression box.

10	Repeat steps 6 - 9 until you've entered all evaluation criteria into the query expression. Press Evaluate.

As you make selections from the input scrolling lists and buttons, an expression builds in the expression box in the Map Query dialog. If you use the mouse to select from the input scrolling lists and buttons, only valid expressions can be created in the expression box. However, if you type directly into the expression box, you can create an invalid expression. Once you make a choice from one of the input scrolling lists or press a button, the error checking is reinstated for the subsequent mouse choices.

To edit the query expression, activate the grid theme created from a previous Map Query. From the Theme menu, choose Edit Theme Expression. The Map query dialog appears, with the current expression that created the grid theme displayed in the expression box. To change the criteria of the expression, highlight the portion of the expression to change, press the delete key on the keyboard, and then type in the desired criteria. To perform another expression, bring up a second Map Query dialog with Map Query in the Analysis menu.

The Not button [image] before an operator evaluates the opposite of the operator. The Parenthesis button [image] allows you to force the sequence of the evaluations within a query. By default, the expression is evaluated from left to right. However, with parentheses, the evaluation will first occur within the parenthesis and then go through the other criteria from left to right. The Update values box, when checked, will retrieve the most current values of the layer chosen in the Layers scrolling list and populate the Unique or Sample Values scrolling list.

The output grid theme from Map Query is automatically named "Map Query" followed by a unique number. The grid data set associated with the output theme is written to the project's working directory, with the name "query" followed by a unique number. Use Properties in the Theme menu to find out which data set is associated with which theme. Use Properties in the Project menu to change the project's working directory. The grid data set associated with the output theme is temporary and is deleted when the theme is deleted. Use Save Data Set in the Theme menu or save the project to prevent the grid data set from being deleted when the theme is deleted.

For additional help on the individual dialog choices, see Map Query (Dialog box).


Frequently asked questions about analysis with the Spatial Analyst
Questions about Analysis with the Spatial Analyst

What do you need help with?

Why are all the values in my output zero?

How do I stop a process that is running for a long time?

Where do my data sets get written?

How do theme and data set names get generated?


Reclassifying the cell values of a grid theme

Reclassify in the Analysis menu changes the values in a grid theme from one value to another through one of two techniques, reclass (for categorical data) or slice (for continuous data). Reclass changes one value to another in a one-to-one value change. For example, while performing a deer-habitat analysis, the values on a land use grid theme, each representing a different type of land use (categorical data), need to be changed to a preference range of 1 to 10. The types of land most preferred by deer are reclassed to higher values and those less preferred to lower values. For instance, the forest land use is reclassed to 10, the low-density residential land use to 5, and the industrial to 1.

Slice considers all values and their distribution in a grid theme simultaneously, and reclassifies the values into a specific number of groups. In the hypothetical analysis of deer habitat, the second theme to the suitability model is based on the preference of deer for locations far from roads. A distance map (continuous data) is created from the existing roads theme. Instead of individually reclassifying each of the thousands of distance values on a 1-to-10 deer preference scale, the values can be sliced into 10 groups. The farthest group receives the highest deer preference value, a value of 10, and the nearest group, a value of 1.

A variation of the reclass reclassification changes cells to and from No Data. In a suitability analysis for siting a housing development, No Data cells are changed to zero so that the cells are included in the model and yet contribute nothing to the cost in the analysis. But cells that fall within the legal buffer of a wetland, which should not be considered under any condition, are set to No Data so that they will not be available as possible building sites.

The output integer grid theme from Reclassify is automatically named "Reclass of" followed by the name of the input theme. The grid data set associated with the output theme is written to the project's working directory, with the name "rclss" followed by a unique number. Use Properties in the Theme menu to find out which data set is associated with which theme. Use Properties in the Project menu to change the project's working directory. The grid data set associated with the output theme is temporary and is deleted when the theme is deleted. Use Save Data Set in the Theme menu or save the project to prevent the grid data set from being deleted when the theme is deleted.

What type of data do you want to reclassify?

Cell values that represent categories

Cell values representing a continuous variable

Null or No Data cell values


Reclassify cell values of a continuous variable
To reclassify cell values of a grid theme representing a continuous variable

1	Activate the continuous grid theme to reclassify.

2	From the Analysis menu, choose Reclassify.

3	Choose the field in the grid theme to classify in the Classification Field dropdown list.

4	By default the Old Values on the reclassification scrolling list are grouped into 9 equal interval classes. To reclassify the input continuous grid theme into more or fewer classes, press the Classify button or type in the desired ranges in the reclassification scrolling list. Separate ranges by a dash (-).

5	In the Classification dialog, choose the type of classification in the Type dropdown list. Specify the number of classes to reclassify the input values into, either by entering the value in the Number of classes type-in box or use the accompanying dropdown list. Identify the precision to use to break classes in the Round values at dropdown list. For more information on the classifications available with the Classification dialog, see Classification (Dialog box).

6	When the reclassification scrolling list is complete, press OK.

Reclassify will always create an integer grid theme.

To add a new record to the reclassification scrolling list (both the Old and New Values being zero), press the Add button [image]. The new record is added under the selected entry or at the end of the list if there's no selected record. You can select a record by clicking on the column to the left of the Old Values column. To delete a record from the reclassification scrolling list, select the record and press the Delete button [image]. When you delete a record, the cells with that value will retain their original values.

A reclassification file can be loaded with the Load button or the existing reclassification specified in the reclassification scrolling list can be saved to a file with the Save button.


Reclassify cell values of categories
To reclassify cell values of a grid theme that represent categories

1	Activate the categorical grid theme to reclassify.

2	From the Analysis menu, choose Reclassify.

3	Choose the field in the grid theme to classify in the Classification Field dropdown list.

4	To perform a one-to-one reclassification change the original values on the reclassification scrolling list (identified in the Old Values column) to the desired value in the New Value column. Any combination of ranges, lists, or single values can be used for the Old Values column. Separate ranges by a dash (-),lists by a comma (,). Edit an entry by clicking on it and typing in the new specification. The New Value can be only a single value or "No Data".

5	When the reclassification scrolling list is complete, press OK.

Reclassify will always create an integer grid theme.

If you desire to assign unique, sequential values (starting with 1) to each of the categorical values, press the Unique button.

To add a new record to the reclassification scrolling list (both the Old and New Values being zero), press the Add button [image]. The new record is added under the selected entry or at the end of the list if there is not a selected record. You can select a record by clicking on the column to the left of the Old Values column. To delete a record from the reclassification scrolling list, select the record and press the Delete button [image]. When you delete a record, the cells with that value will retain their original values.

The Lookup button can be used to create a grid theme with values of one of the fields in the input grid theme. This can be used to create a grid theme of pH values from a grid theme of soil types that has pH as a field in its table.

A reclassification file can be loaded with the Load button or the existing reclassification specified in the reclassification scrolling list can be saved to a file with the Save button.

By pressing the Classify button, the classification method can be changed in the Type dropdown list, the number of classes in the Number of classes type-in box, and the precision of the output values from the Round values at dropdown list. For more information on the classifications available with the Classification dialog, see Classification (Dialog box).


Reclassify null cell values
To reclassify the null or No Data cell values of a grid theme

1	Activate the grid theme with the No Data values to reclassify.

2	From the Analysis menu, choose Reclassify.

3	Choose the field in the grid theme to classify in the Classification Field dropdown list.

4	To change a value or values to No Data type in "No Data" in the New Values column for those values you wish to change. To change No Data to a value change the No Data record in the New Values column to the desired new value.

5	When the reclassification scrolling list is complete, press OK.

Reclassify will always create an integer grid theme.


Setting the analysis properties
Setting the analysis properties for a view

Frequently, some of the area covered by a grid theme is of no interest during analysis. You may want to analyze a group of cells meeting specific requirements, or need a certain resolution of the results, or even just want to cover a smaller area. The Spatial Analyst has three parameters for just these three things - cells to process within the extent (the mask), cell size, and extent in which to perform processing.

Once set, each parameter determines the characteristic of the resultant output grid themes from operations found in the Analysis menu. The analysis properties apply only to the active view. Different views in the same project can have different analysis environment settings, which are set with Properties in the Analysis menu.

Which analysis environment parameter would you like to set?

The extent

The cell size

A mask


Technical notes about the ArcView Spatial Analyst extension v.1.1
Technical notes about the ArcView Spatial Analyst extension v1.1

Drawing integer grid themes

I can't draw a particular integer grid theme. Why?

The range of values in that grid theme's Value Attribute Table (VAT) exceeds 1 million.

To fix the problem you can convert the integer GTheme to a floating point GTheme with the Map Calculator, or Reclassify the GTheme to a range less than 1 million. Classifications on the Legend will not work. This only affects display and an integer GTheme with a range over 1 million can still be used in analysis steps.

Running out of swap space

I sometimes run out of swap space when interpolating a surface or creating contours from a point theme. Why?

Creating contours from a point theme involves interpolating a temporary surface so we can create contours.  Interpolation requires more and more swap space as the resolution of the output grid and the number of points to interpolate from increases.  A workaround for interpolating a surface from large point themes is to increase the swap space of your machine.

Grid data set pathnames

I have grid data sets in a directory on my machine, but ArcView does not recognize them.

ArcView will not recognize grids located in paths containing periods (".") or spaces (" ").  Remove the offending characters or use the operating system's file manager to move the directory containing the grid directories and associated Info directory to a different location. (Do not move, copy, rename, or delete grid directories themselves with the operating system's file manager. Always use the ArcView Spatial Analyst's Grid Manager located under the File menu when a view is active to manage grid data sets).

Writing grid data sets (UNIX)

ArcView will not write newly created grid data sets to the working directory that I have specified.

On UNIX based platforms, ArcView will not write grid data sets to directories that contain capital letters.

Histogram table creation location

When creating a Histogram the associated table is written to the $TMPDIR directory on UNIX platforms and the $TEMP directory on Windows NT and Windows 95 platforms.  On UNIX platforms, when the $TMPDIR environment variable is not set, the table is written to the /tmp directory, rather than the working directory.  On the supported PC platforms, when the $TEMP environment variable is not set, the table is written to the $HOME location.

Integer grid theme with no Value Attribute Table

When you have more than 500 unique values and the range of values is greater than 100,000 the resulting integer grid theme will not have an associated table by default. Grid themes created from 1-bit image themes will also not have an associated table by default. A table can be created with the BuildVAT request (only for integer grids).

Error message when exiting ArcView after using Spatial Analyst

I sometimes get the error message NOT OWNER OF DIRECTORY, FILES REMOVED AS PERMITTED when exiting ArcView. Why?

This error message will appear when exiting ArcView at the same time that a temporary grid is still drawing. When this happens, this temporary grid’s directory will remain on disk, however, in a unusable state as all of its associated Info files are deleted. If desired, the remaining directory can simply be removed with your operating system’s file manager.

Fields that get exported to a shapefile

When I export my grid to a shapefile, only the value attributes are brought over into the shapefile's table (in the Gridcode field).  The rest of the fields of the Value Attribute Table of the grid are not in the new shapefile.

If you want additional attributes attached to the shapefile, join the attributes of the Value field of the Grid's VAT to the Gridcode field of the new shapefile, using the table joining capabilities of the Table document.

Source Manager

It takes a long time to switch drive letters when I use the Source Manager.

This process can take some time depending on your network, and how many root level directories you may have. The Source Manager must check every directory structure at each level you choose to see if it is a grid or not. When looking for shapefiles, the Source Manager tends to be quicker. Also, to speed changing directories, simply type the desired pathname directly into the name input field.

Converting an image to a grid

I can't convert my image to a grid. Why not?

Either you are trying to convert an image with a world file that contains rotation, you have added a grid data source as an image rather than a grid, or your image theme is an image catalog.  These cases are not supported by ArcView.

Selecting cells in a grid theme

I can't select features in a grid theme on a view like I can with a theme based on a shapefile. Why not?

Since every cell in an integer grid theme does not have a separate record in its table, you are not able to select cells directly in the view. If you were to select a cell in the view it would select the record containing the value of the cell in the table. Since this same record is used for multiple cells, then all cells with this value would then be selected in the view. To prevent this confusion, selection on an integer grid theme can only be made from the table.  This is the reason that the enable select features tool, and the zoom to selected button are not highlighted when a grid theme is active.

Printing transparent cells when using a brightness theme

When I attempt to print my view which contains a grid that has transparent cells and has a brightness theme applied to its display, I get the error "Invalid Transparent Mode during Multi Band Display".  Why ?

When you display your grid like this, ArcView is rendering a multi-band image of your grid into the view. ArcView's Enhanced and Basic postscript printer drivers do not support transparent areas in multi-band images and this is why you are getting the error. Simply removing the transparency defined in the legend will allow this to work. However, sometimes this is not an option.

As a workaround, use the Native OS printer driver choice on the Print menu in the PostScript Interface section. Also, Native OS printer drivers usually create much larger files than ArcView's drivers and your printer may not have enough memory. If your printer does not support transparent multi-band images, or have enough memory, then you will have to upgrade your printer and/or printer driver.

Interpolation

I want to use all of the points in my interpolation but they are not all considered.

Points on the edge of the analysis window aren't used in the interpolation. As a workaround, increase the extent of the new surface with the Analysis Properties or with the Output Grid Specification dialog.

Extended shapefiles

Versions of core ArcView beyond version 3.0a (3.0b for UNIX) and the 3D Analyst offer access to create and work with extended shapefiles (3D and measured shapes).  The Spatial Analyst v1.1 can not access extended shapefiles when loaded while running ArcView 3.0a (3.0b for UNIX).  However, the Spatial Analyst v1.1 can access extended shapefiles when loaded while running ArcView 3.0a (3.0b for Unix) if the 3D Analyst is also loaded.  The Spatial Analyst v1.1 can also access extended shapefiles when loaded while running ArcView 3.1.

Exporting grids to ASCII and binary files

I exported one grid to an ASCII file (*.asc) and another grid to a binary file (*.flt). Both grids had a projection already set. I used the default naming conventions in ArcView and now my ASCII grid file has the projection file (*.prj) of the binary grid file.

Exporting projected grids have potential to overwrite .prj information as the ASCII and binary default naming conventions have similar prefixes. It is a good habit to uniquely name the files you create.

Charts: transparent classes

My grid theme has transparent colored classes in my view's Table of Contents and when I create a histogram or other kind of chart, the transparent classes are now black.

 	This is a limitation in ArcView's charts.  As a workaround, those classes can be manually changed from black to transparent.

Charts: using to show selected cells

When I create a chart or histogram from my grid, and then select each of the bars, the corresponding grid cells don't flash to show their location like a shapefile or coverage vector theme does. Why not?

This is not a feature of the ArcView Spatial Analyst.

Histograms and graphics

My histogram seems to be counting cells twice. Why?

When performing histograms from the underlying cells from overlapping selected graphics, you will notice that those overlapped cells will be counted twice.

When I select 2 sets of graphics, union them, and then attempt to perform a histogram based on the cells underneath that graphic entity, I get an “Unable to continue” error message.  Why?

This operation is not supported by the Spatial Analyst.  To get the desired results, simply select the desired multiple graphics and then perform the histogram, without using the union.

GTheme.MakeQueryMap

I get a syntax error when I use GTheme.MakeQueryMap directly from a Script Editor.

  	GTheme.MakeQueryMap will give a Syntax error if invoked from a Script Editor window.  It must be invoked from a View's menu, button or tool.

Zones with large values

Certain functions such as Tabulate Areas, Summarize Zones, and Histogram by Zone may generate a Memory Error due to the zones possessing large values.

As a workaround, simply decrease the values of the zones.

Null values

Can I set null values for any field in a Grid Theme’s table (VAT)?

No, since grids have a predefined null value that is set for the Value field, it cannot be used or changed. However, you can reclassify Grid Themes using the Reclassify option from the Analysis menu to change values to No Data (null) values, values to other values, No Data Values to values, etc.

aGrid.BuildVAT instance request

I can’t build a Value Attribute Table (VAT) for my grid that does not have one.

Floating Point valued grids can not have a VAT built for them. You can tell if your grid is of type floating point by looking in the Properties dialog on the Theme pulldown menu.

Grid.Make class request

I get an error message when I use the Grid.Make class request.

This is due to the fact that you need to create the necessary source name argument (aSrcName) with the Grid.MakeSrcName instance request rather than the SrcName.Make class request.

Analysis properties and projections

Always set the projection of a view before you set the Analysis Properties.  If you do not, you may run the risk of using Analysis Properties that are based on non-projected extents and cell sizes.

Grid theme legend files

Loading a previously saved grid legend (gridfn.avl) into a different theme type is not supported.  Be sure to only load grid legends into grid themes (GThemes).


Using the map calculator
To use the map calculator

1	From the Analysis menu, choose Map Calculator.

2	The Map Calculator dialog aids in the creation of an expression that produces a new output grid theme. The expression can be based on a single grid theme or multiple grid themes. To aid in the creation of the expression, there are five groups of inputs in the Map Calculator dialog. The first is the Layers scrolling list which identifies the available grid layers in the active view; the second, arithmetic operator buttons; the third, a keypad of numbers; the fourth, a group of relational and Boolean operators; and the fifth, a series of mathematical functions. A typical sample session follows.

3	Double-click on a layer from the Layers scrolling list.

4	Press one of the arithmetic operators (e.g., *, /, -, and +).

5	Press the appropriate numbers on the keypad to apply to the values of the input layer using the arithmetic operation.

6	Press another arithmetic operator.

7	Choose a second layer from the Layers scrolling list.

8	Choose a mathematical functional group from the dropdown list to the far right of the Map Calculator (e.g., Logarithms, Arithmetic, Trigonometric, or Power).

9	Choose one of the mathematical buttons that appears in the mathematical function group of buttons.

10	Repeat steps 6 - 9 until you've entered all components of the expression. Press Evaluate.

As you make selections from the input scrolling list and buttons, an expression builds in the expression box in the Map Calculator dialog. If you use the mouse to select from the input scrolling list and buttons, only valid expressions can be created in the expression box. However, if you type directly into the expression box, you can create an invalid expression. Once you make a choice from one of the input scrolling list or press a button. the error checking is reinstated for the subsequent mouse choices.

The Map Calculator can create simple expressions with a single function or complex with many operations and functions.

Mathematical operators apply a mathematical operation to the values in two or more input grid themes; mathematical functions apply a mathematical function to the values in a single input grid theme. There are three groups of mathematical operators in the Map Calculator: Arithmetic, Boolean, and Relational.

 Arithmetic Operators - The Arithmetic operators (*, /, -, +) allow for the addition, subtraction, multiplication, and division of two grid themes, or numbers, or combination of the two.

 Boolean Operators - The Boolean operators (And, Not, Or, and Xor) use Boolean logic (TRUE or FALSE) on the input values. Output values of TRUE are written as 1 and FALSE as 0.

 Relational Operators - The Relational operators (<, <=, <>, =, >, and >=) evaluate specific relational conditions. If the condition is TRUE, the output is assigned 1; if the condition is FALSE, the output is assigned 0. In an avalanche study, a relational operator can be used to show the areas of highest avalanche risk by identifying all cells that are greater than 5,000 meters.

There are four subgroups of mathematical functions: Logarithms, Arithmetic, Trigonometric, and Powers.

 Logarithm - The Logarithm functions perform exponential and logarithmic calculations on input grid themes and numbers. The base e [image], base 10 [image] and base 2 [image] exponential capabilities and the natural log [image], base 10 [image], and base 2 [image] logarithmic capabilities are available.

 Arithmetic - The Abs button [image] takes the absolute value of the values in an input grid theme, Two rounding functions, the Ceil [image] and Floor [image] buttons, convert decimal-point values into whole numbers. The Int [image] and Float [image] buttons convert values from and to integer and floating-point values. And, the IsNull button [image] returns 1 if the values on the input theme are No Data, and 0 if they are not.

 Trigonometric - Trigonometric functions perform various trigonometric calculations on the values in an input grid theme. The sine [image], cosine [image], tangent [image], inverse sine [image], inverse cosine [image], and inverse tangent [image] functions are available.

 Power - The square root [image] of the values on the input grid layer can be calculated, the square [image] determined, or the values can be raised to a power [image].

To edit the expression of a grid theme, activate the grid theme created from a previous map calculation. From the Theme menu, choose Edit Theme Expression. The Map Calculator dialog appears, with the current expression that created the grid theme displayed in the expression box. To change any of the components of the expression, highlight the portion of the expression to change, press the delete key on the keyboard, and then type in the desired component. To perform another expression, bring up a second Map Calculator dialog with Map Calculator in the Analysis menu.

The Not button [image] before an operator evaluates the opposite of the operator. The Parenthesis button [image] allows you to force the sequence of the evaluations within an expression. By default, the expression is evaluated from left to right. However, with parentheses, the evaluation will first occur within the parenthesis and then go through the other criteria from left to right.

The output grid theme from Map Calculator is automatically named "Map Calculation" followed by a unique number. The grid data set associated with the output theme is written to the project's working directory, with the name "calc" followed by a unique number. Use Properties in the Theme menu to find out which data set is associated with which theme. Use Properties in the Project menu to change the project's working directory. The grid data set associated with the output theme is temporary and is deleted when the theme is deleted. Use Save Data Set in the Theme menu or save the project to prevent the grid data set from being deleted when the theme is deleted.

For additional help on the individual dialog choices, see Map Calculator (Dialog box).


To set the analysis cell size
To set the analysis cell size for a view

1	From the Analysis menu, choose Properties.

2	Set the analysis cell size. There are three ways to set the cell size; 1) from the Analysis Cell Size dropdown list choose either Minimum Of Inputs, Maximum Of Inputs, Current Value, or Same As one of the grid themes in the view; 2) type in a numeric cell size in the Cell Size type-in box; or 3) type in the number or rows and columns for output grid themes in the Number of Rows and Number of Columns type-in boxes. Press OK.

The Analysis Cell Size can be set to the following

 Minimum Of Inputs - will set the output cell size to the finest resolution of the grid themes entered into an operation in the Analysis menu.

 Maximum Of Inputs - will set the output cell size to the coarsest resolution of the grid themes entered into an operation in the Analysis menu.

 As Specified Below - will set the output cell size to what is typed into the Cell Size type-in box or the number of rows and columns typed into the Number of Rows and Number of Columns type-in boxes.

 Current Value - will reset the cell size to the value that was set when the dialog was brought up.

 Same As <Grid Theme> - will set the output cell size to the resolution of a grid theme in the view.

Maximum Of Inputs is the default analysis cell size setting.


To set the analysis extent
To set the analysis extent for a view

1	From the Analysis menu, choose Properties.

2	Specify the analysis extent. There are two ways to identify the analysis extent; 1) from the Analysis Extent dropdown list choose: Same As View, Same As Display, Intersection Of Inputs, Union Of Inputs, Current Value, or Same As a theme in the view; 2) type in the lower left and upper right of the analysis extent in map units in the Left, Top, Bottom, and Right type-in boxes. Press OK.

The Analysis Extent can be set to the following

 Same As View - will set the analysis extent equal to the extent of the view.

 Same As Display - will set the analysis extent equal to the current extent of the display. If you change the extent of the display after setting the analysis properties the analysis extent will not change.

 Intersection Of Inputs - will set the analysis extent to the common area shared by the input grid themes of an operation in the Analysis menu.

 Union Of Inputs - will set the analysis extent equal to the minimum extent to cover all the input grid themes of an operation in the Analysis menu.

 As Specified Below - will set the analysis extent to the extent typed into the Left, Top, Bottom, and Right type-in boxes.

 Current Value - will reset the extent to the value that was set when the dialog was brought up.

 Same As <Theme> - will set the analysis extent to the extent of a theme in the view.

To graphically specify the analysis extent from the view display, first choose the Zoom In tool [image]. Define the area you want to set the analysis extent to. in the Analysis Properties dialog, choose Same As Display in the Analysis Extent dropdown list.

Union Of Inputs is the default analysis extent setting. Setting the analysis extent has no effect on the display extent of the view.


What is the analysis mask
To set an analysis mask for a view

1	From the Analysis menu, choose Properties.

2	From the Analysis Mask dropdown list, choose a grid theme as the mask or choose No Mask Set. Press OK.

A mask allows processing to occur only for specified cells within the analysis extent. The mask grid theme should contain No Data for those areas where processing should not occur and any value for the cells to be processed. You can convert feature themes to grid themes with Convert to Grid in the Theme menu so that they can be used as masks. Make sure that areas you want masked out have No Data values. You can use Map Query in the Analysis menu to create mask grid themes. Since areas in the output grid theme that don't meet the query specified are given a value of 0 you must convert them to No Data. You can use Reclassify in the Analysis menu to change cell values to No Data.

If you wish to process all cells within the analysis extent, choose No Mask Set. No Mask Set is the default analysis mask setting.


What is the ArcView Spatial Analyst
What is the ArcView Spatial Analyst?

The ArcView Spatial Analyst is a tool for helping you discover and understand spatial relationships in your data. This discovery and understanding can be as simple as viewing and querying your data or as complex as creating an integrated custom application.

The main component of the Spatial Analyst is the grid theme. The grid theme is the raster equivalent of the feature theme. The Spatial Analyst also presents generic spatial analysis functionality on grid and feature themes, that is added to ArcView as an extension that is loaded with Extensions in the File menu when the project window is active. The user interface components of the Spatial Analyst are loaded into the interface for views.

With the Spatial Analyst, you'll be able to perform the following functions found on the Analysis menu:

Find Distance

Assign Proximity

Calculate Density

Cell Statistics

Summarize Zones

Histogram By Zone

Tabulate Areas

Map Query

Map Calculator

Neighborhood Statistics

Reclassify

The following functions are found on the Surface menu:

Interpolate Grid

Create Contour

Derive Slope

Derive Aspect

Compute Hillshade

Calculate Viewshed

The following functions are added to the Theme menu:

Convert to Shapefile (not added, but modified to work with grid themes)

Convert to Grid

Save Data Set

Edit Theme Expression

The following functions are added to the File menu:

Manage Data Sources

Import Data Source

Export Data Source

The following functions are added as buttons and tools:

 Histogram button

 Contour tool

Much more functionality is accessible via Avenue, such as hydrological analysis and geometric transformations, just to name a few. Search the on-line help index on "grid" to find the Grid (Class) topic to find out all the functionality available through Avenue for the Spatial Analyst.


What's new in the Spatial Analyst v1.1

The most noticeable change with version 1.1 of the Spatial Analyst is the new menu interface. This was changed to coincide with the new 3D Analyst Extension. Instead of just having an Analysis menu, the surface related options have all been moved over into a Surface menu. This version of the Spatial Analyst has been released at the same time as the 3D Analyst so that they may be loaded and used at the same time. Prior versions of Spatial Analyst will not load properly when the 3D Analyst is loaded.

This version of the Spatial Analyst also adds Calculate Viewshed (Visibility request) to the Surface menu. Also, the Visibility request now respects the Analysis properties.

The Grid Manager choice on the File menu has been renamed to Manage Data Sources. The new Source Manager provides management for shapefiles as well as grids now.

Also, in this version there are 4 new requests. These are as follows:

Grid.CalcPolynomialFit - Performs a linear least-squares fit to a list of links.

aGrid.StreamToPolyLineFTab - Converts a linear network to a polyline shapefile.

aGrid.AsPointFTab - Converts a grid to a point shapefile.

aGrid.AsPolyLineFTab - Converts a grid to a polyline shapefile.


Why are all the values in my output zero
Why are all the values in my output zero?

 Find Distance - All of the cells in the input grid theme have a value other than No Data and there's no selected set in the theme. Find Distance calculates a distance value for each cell that has a No Data value if there's no selected set. If there is a selected set, then a distance value is calculated for each cell that's not selected.

 Calculate Density - If your input was in decimal degree coordinates, then the density values are very small. The legend rounds numbers to 3 places past the decimal point by default. Since the values are so small they are all rounded to zero. Use Properties in the View menu to set a projection for the view or increase the precision used to round values with the Classify button of the Legend Editor.

 Analysis Extent - If the analysis extent set for a view doesn't overlap any part of the extent of any of the inputs to an operation, then you will get a grid theme of all zeros or No Data values.