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Compute Hillshade

Computes illumination values for a grid or TIN based surface.

Creates a grid theme as output. Each cell in the output grid theme represents the illumination at that location on the surface, based on the direction of the sun (azimuth) and its height in the sky (altitude).

Available when a single grid or TIN theme is active.

Use only on grid or TIN themes representing a continuous attribute, such as elevation or density.

TIN themes can only be present when the 3D Analyst extension installed.


Contour Tool

 Creates a line of constant value, a contour line, from a point selected on a grid or TIN theme.

The contour is presented as a graphic attached to the theme it was created from. The graphics are visible when the theme is visible. The value of the contour line is displayed on the left side of the message bar.

If a line theme is editable, then the contours will be written into this theme. A field will be added to the line theme and the value of the contour will be added to it.

Available when a single grid or TIN theme is active.

Use only on themes representing a continuous attribute, such as elevation or density.

TIN themes are available only when the 3D Analyst extension is installed.


Convert to Grid

Converts the selected features of each active theme to a grid theme. If the active theme doesn't contain a selected set, all features in the active theme are converted.

An image theme with multiple bands will be converted into multiple grid themes, one grid theme per band.

A TIN theme will have heights interpolated for the center-cell position of all cells in the output grid. Those positions in the input TIN that have NODATA will be coded NODATA in the corresponding cells in the output grid.

Available when one or more themes are active.

To convert a database theme to a grid theme, you must first export it to a shapefile with Convert to Shapefile in the Theme menu.

To create a grid theme containing only a subset of the values in the original grid theme, select the values you want, then use Convert to Grid. Cells selected in the original grid theme will retain their value. Cells not selected will be converted to No Data.


Create Contours

Creates lines of constant value, contours, on a point, grid, or TIN theme using a specified interval, both above and below a specified base value.

Each line of the shapefile created represents the locations with the same height, magnitude, or concentration of the values of the input theme.

If the input is a point theme, a temporary gridded surface will first be interpolated before the contours are created.

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

Use only on themes representing a continuous attribute, such as elevation or density.

TIN themes are available only when the 3D Analyst extension is installed.


Derive Aspect

Calculates aspect for each cell of a grid theme or triangle of a TIN theme.

Creates a grid theme as output. Each cell in the output grid theme represents the direction of maximum slope of the input grid or TIN theme. Aspect values will be continuous, starting at 0 degrees (north) and increasing clockwise until 360 degrees is reached at north again.

When the input is a grid theme, aspect is calculated for each cell using a 3x3 window.

When the input is a TIN theme, aspect for each output grid cell is calculated by determining the aspect of the triangle its center falls in. TIN themes are available only when the 3D Analyst is installed.

Available when a single grid or TIN theme is active.

Use only on themes representing a continuous attribute, such as elevation or density.


Derive Slope

Calculates the rate of maximum change for locations on grid or TIN themes.

Creates a grid theme as output. Each cell in the output theme contains a continuous slope value represented in degrees.

When the input is a grid theme, the rate of maximum change for each cell to its neighbors is calculated using a 3 by 3 window.

When the input is a TIN theme, the slope for each output cell is calculated by using the triangle its center falls in. TIN themes are available only when the 3D Analyst extension is installed.

Available when a single grid or TIN theme is active.

Use only on themes representing a continuous attribute, such as elevation or density.


Export Grids
Export Data Source

Converts grid data sets to either an ASCII or IEEE floating-point file format.

The output file formats can be used to pass data created with ArcView to other applications that don’t read ESRI’s grid data structure.


Import Grids
Import Data Source

Converts ASCII, IEEE floating-point, USGS DEM, and US DMA DTED files to grid data sets. Additionally, when the 3D Analyst Extension is loaded ASCII 3D generate files can be converted to 3D shapefiles.


Interpolate Surface
Interpolate Grid

Fills in the gaps of a point theme by analyzing the points around each location to create a continuous surface.

Creates a grid theme as output. Each cell in the output grid theme represents the value on a surface at that location according to the surrounding points. The Interpolate Surface dialog that is displayed with this operation gives you control over how the points are analyzed to create these values.

Available when a single point or multipoint theme is activate.

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


Interpolate Surface Dialog
Interpolate Surface (Dialog box)

Interpolates a value for a cell, using the surrounding points in a point theme, according to the parameters you set here.

Dialog box options

Z Value Field   A dropdown list for choosing the field that contains the attribute you’re interested in. Only numeric fields in the point theme will be displayed.

The value of Z Value 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.

Method   A dropdown list for choosing a method to give values to areas that don’t contain points. The two different methods are IDW and Spline.

Which method do you want information on?

IDW

Spline


Interpolate Surface Dialog IDW
IDW (Dialog box)

Gives values to each cell in the output grid theme by weighting the value of each point by the distance that point is from the cell being analyzed and then averaging the values.

Dialog box options

Nearest Neighbors   Uses the N nearest points to the cell being analyzed. Type in a value for N in the No. of Neighbors type-in box.

Fixed Radius   Uses all points within a distance of the cell being analyzed. Type in a value for the distance in the Radius type-in box. If the distance units for the view are set, then the distance will be in distance units. If the distance units are not set, then the distance will be in map units.

Power   The exponent of distance used in the calculation. Controls the significance of surrounding points on the value given to the cell being analyzed. A higher power results in less influence from distant points.

Barriers   Used to limit certain points from being used in the calculation of a new value for a cell, even if the point is one of the nearest neighbors or within a certain distance. You wouldn't want to use an elevation point on one side of a ridge to create an elevation value on the other side of the ridge. Barriers can be

 No Barriers

 <Line Theme> - Sets the barriers to whichever line theme you choose in the view.


Interpolate Surface Dialog Spline
Spline (Dialog box)

Fits a curve through the points surrounding the cell being analyzed and gives the cell the value of the curve at that location.

Dialog box options

Type   The type of curve fitting. Type can be

 Regularized - Creates a smoother flowing surface.

 Tension - Results in a more rough surface that tightly conforms to the input data points.

Weight   Controls the tautness of the curves. As the Weight increases with the Regularized Type, the output surface will become increasingly smoother. With the Tension Type, increasing the Weight will cause the surface to become stiffer, eventually conforming closely to the input points.

No. of Points   The number of nearest points around the cell being analyzed that will be used to fit the curve.


Manage Grids
Manage Data Sources

Allows you to delete, copy, and rename data sets.

Never delete, copy, or rename grid data sets using the computer's file system commands. Use ArcView to do this.


Output Grid Specification Dialog
Output Grid Specification (Dialog box)

Displays the properties that will be used to create output during an operation on a feature theme. The following properties can be viewed and changed.

 The spatial extent.

 The cell size, or resolution.

Dialog box options

Output Grid Extent   The spatial extent for the output theme. The Output Grid Extent can be set to

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

 Same As Display - Sets extent to the extent of the display.

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

Output Grid Cell Size   Sets the resolution that will be used to create the output grid theme. This option is only available when the view contains one or more grid themes. The Output Cell Size can be set to

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

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

Cell Size   The cell size to be used for output grid theme.

Number of Rows   The number of rows that the output grid theme will created with.

Number of Columns   The number of columns that the output grid theme will be created with.


Save Data Set

Creates a permanent grid data set on disk from a grid theme which has a data set in a temporary state. Since data sources of grid themes created from analysis are temporary, they will be deleted if you delete the grid theme before saving the project.

Available when an active grid theme has a data set in a temporary state.


Viewshed
Calculate Viewshed

Calculates the areas on a surface that are visible from one or more observation points.

The surface is represented by a grid or TIN theme. The observation points are represented by the points in a point theme or the vertices of lines in a line theme. Selected points or lines are used if there is a selection, otherwise all features are used.

The output is a grid with cells assigned visibility codes. Those assigned a value of 0 are not visible from any observation point. Those assigned values greater than 0 can be seen by that many points.


About the ASCII raster file format
The ASCII raster file format

The ASCII raster file format is a simple format that can be used to transfer raster data between various applications. It is basically a few lines of header data followed by lists of cell values. The header data includes the following keywords and values:

 ncols - number of columns in the data set.

 nrows - number of rows in the data set.

 xllcenter or xllcorner - x-coordinate of the center or lower-left corner of the lower-left cell.

 yllcenter or yllcorner - y-coordinate of the center or lower-left corner of the lower-left cell.

 cellsize - cell size for the data set.

 nodata_value - value in the file assigned to cells whose value is unknown. This keyword and value is optional. The nodata_value defaults to -9999.

For example,

ncols 480

nrows 450

xllcorner 378923

yllcorner 4072345

cellsize 30

nodata_value -32768

43 3 45 7 3 56 2 5 23 65 34 6 32 etc

35 45 65 34 2 6 78 4 38 44 89 3 2 7 etc

etc

The first row of data is at the top of the data set, moving from left to right. Cell values should be delimited by spaces. No carriage returns are necessary at the end of each row in the data set. The number of columns in the header is used to determine when a new row begins. The number of cell values must be equal to the number of rows times the number of columns.

The ASCII raster file format can only be imported or exported using the Spatial or 3D Analysts.

  Related topics


About the binary raster file format
The binary raster file format

The binary raster file format is a simple format that can be used to transfer raster data between various applications. It consists of two files, the IEEE floating-point file and a supporting ASCII header file. The header file must have the same name as the data file, but with a .hdr file extension. The header data includes the following keywords and values:

 ncols - number of columns in the data set.

 nrows - number of rows in the data set.

 xllcenter or xllcorner - x-coordinate of the center or lower-left corner of the lower-left cell.

 yllcenter or yllcorner - y-coordinate of the center or lower-left corner of the lower-left cell.

 cellsize - cell size for the data set.

 nodata_value - value in the file assigned to cells whose value in unknown. This keyword and value is optional. The nodata_value defaults to -9999.

 byteorder - the byte order of the binary cell values. You can choose between two keywords, msbfirst or lsbfirst. Msbfirst is used for cell values written with the most significant bit first. Lsbfirst is used for cell values written with the least significant bit first.

For example,

ncols 480

nrows 450

xllcorner 378923

yllcorner 4072345

cellsize 30

nodata_value -32768

byteorder msbfirst

The data file will be a matrix of 32 bit signed IEEE floating-point values. The file will have a line of binary numbers for each row in the data set. The first line of data is the top row of the data set, moving from left to right.

The binary raster file format can only be imported or exported using the Spatial or 3D Analysts.

  Related topics


About the USGS DEM raster file format
The USGS DEM raster file format

A USGS DEM file is a raster data set representing the surface of the earth.

Standard USGS 7.5-minute, 1-degree, or any other file in USGS DEM format is supported. The file can be in either fixed or variable record length format.

Don't use USGS DEM data that has horizontal units in decimal seconds with slope, hillshade, visibility, and curvature. Project it into a planar coordinate system with a package such as ARC/INFO before using any of the above functions.

Digital terrain data covering most regions in the United States is available in the USGS DEM format from the U. S. Geological Survey. For more information, write the National Cartographic Information Center, 507 National Center, Reston, VA  22092. More information can also be found on the World Wide Web at the USGS node of the National Geospatial Data Clearinghouse site found at http://nsdi.usgs.gov/nsdi/.

The USGS DEM file format can only be imported using the Spatial or 3D Analysts.

  Related topics


About the US DMA DTED raster file format
The US DMA DTED raster file format

A United States Defense Mapping Agency Digital Terrain Elevation Data file is a raster data set representing the surface of the earth.

Only DTED data distributed on CD-ROM is supported. All DTED Level II data is distributed on 9-track tape and isn't supported.

Don't use DTED data that has horizontal units in decimal seconds with slope, hillshade, visibility, and curvature. Project it into a planar coordinate system with a package such as ARC/INFO before using any of the above functions.

Refer to Military specification MIL-D-89020 for further information.

The US DMA DTED raster file format can only be imported using the Spatial or 3D Analysts.

  Related topics


Adding a grid theme to a view
To add a grid theme to a view

1	Activate the view you want to add the grid theme to.

2	Press the Add Theme button [image]. This will bring up the Add Theme dialog.

3	Change the Data Source Type dropdown list to Grid Data Source in the Add Theme dialog.

4	Navigate to the directory that contains the grid data source you want to add as a theme.

5	Select the grid data source and press the OK button in the Add Theme dialog. The grid data source will be added to the active view as a grid theme with a default legend.


Altering brightness by compositing to provide depth
To alter the brightness of a grid theme

1	Double-click on a grid theme's legend in the Table of Contents to open the Legend Editor.

2	Press the Advanced button in the Legend Editor.

3	Select a Brightness Theme from the dropdown list of grid themes in the view.

4	Alter the Minimum and Maximum Cell Brightness values, if desired.

5	Press OK in the Advanced Options dialog.

6	Press Apply in the Legend Editor.

Varying the brightness of the color used to display each cell in a grid theme with the value of another grid theme can help give depth to your display. You will not only be able see how one variable is spatially distributed, but how another variable changes within that variable. This is useful for seeing the relationship between two grid themes, such as land use and topography. Topography is not the only type of information you can use as a brightness theme. Any continuous data set, such as distance, density, and percent-cover, can be used.

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 allows lower values to be brighter than higher values in the brightness theme. 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 or 100 will result in the colors of black and white respectively in areas where the brightness theme has low and high cell values . If you don’t want to totally wash out your colors, use a lower number than 100. If you want at least a small amount of color to be displayed, use a higher number than 0.


Cells that have a specified attribute
To show all cells that have a specified attribute in a grid theme

From the table

1	Click on an integer grid theme to make it active, then press the Open Theme Table button [image].

2	Click the Select tool [image].

3	Click on a cell value record in the table. This will highlight the record in the table. Cells that contain the selected value will also be highlighted in the view. To select more that one cell value at a time, hold down the shift key on the keyboard while clicking on several cell values in the table.

From the Query Builder

1	Click on a integer grid theme to make it active.

2	Press the Query Builder button [image].

3	Formulate your query with the Query Builder. Cells with the selected values will also be highlighted in the view.

Selected cells and records will be highlighted in the selection color for the project. You can change this color in the Project Properties dialog, which comes up when you choose Properties in the Project menu.

Unlike feature themes, where you can select features from the view or table, grid themes can only have cell values selected from the table. Since many cells may be referenced by the same value in the table, selecting cells from the view is not possible.


Changing the colors used to display cell values
To change the colors used to display cell values

There are two possible types of legends for grid themes, unique values or graduated colors. All grid themes can use the graduated colors type of legend. Only integer grid themes can use the unique values legend type.

To create a Unique Values legend for a grid theme:

1	Double-click on a grid theme's legend in the Table of Contents to open the Legend Editor.

2	Choose Unique Value as the type of legend.

3	Choose a Values Field from the dropdown list of fields.

4	Choose a Color Scheme or create your own symbology.

5	Press Apply.

To create a Graduated Colors legend for a grid theme:

1	Double-click on a grid theme's legend in the Table of Contents to open the Legend Editor.

2	Choose Graduated Color as the type of legend.

3	Choose a Classification Field from the dropdown list of fields. ArcView automatically makes a equal interval classification of 9 classes and applies a default color ramp.

4	Optionally change the classification of the legend through the Classify button.

5	Choose a Color Ramp or create your own symbology.

6	Press Apply.

For more information on working with the Legend Editor, see the topics under the "Choosing colors and symbols" section in the "Creating and using maps" section of the Help Topics Contents.


Choosing an appropriate legend type

To choose an appropriate legend type, you need to understand what the cell values contained in your grid theme represent. Cell values can represent one of two data value types, discrete and continuous. Discrete data will always be stored as an integer grid theme. Continuous data can be stored as either an integer or floating point grid theme. Discrete values represent phenomena in categories. Examples of discrete value types are state names, land use type, soil type, zip codes, road types, and land ownership. Continuous values represent phenomena along a range. Examples of continuous value types are population density, pH, average income, speed limits, elevation, and the price of land.

Are your grid data values discrete, like soil type or zip code boundaries?

Use a Unique Values legend.

Are your grid data values continuous, like elevation or population density?

Use a Graduated Colors legend.

A continuous variable may be stored in discrete areas on your grid theme, such as average household income within tract boundaries. You would still want to use a Graduated Colors legend to symbolize this grid theme.


Computing hillshade from a surface
To compute hillshade from a surface

1	Activate the grid or TIN theme on which to compute the hillshade in a view or 3D scene.

2	From the Surface menu, choose Compute Hillshade.

3	Enter where the illumination source is in relation to the input grid or TIN theme in the Azimuth type-in box.

4	Enter the slope or angle of the illumination source above the horizon in the Altitude type-in box. Press OK.

5	If the input theme is a TIN, specify the output extent in the Output Grid Extent dropdown list, the cell size in the Output Grid Cell Size Input field, and the number of rows and columns in the Number of Rows and Number of Columns input fields on the Output Grid Specification dialog. Press OK.

Compute Hillshade is used to determine the hypothetical illumination of a surface as part of an analysis step or for graphical display. For analysis, Compute Hillshade can be used to determine the length of time and intensity of the sun in a given location. For a graphical display, Compute Hillshade can greatly enhance the relief of a surface when the output is used as the brightness theme for the display of another grid theme. This can be done with the Advanced button in the Legend Editor.

Various features in the input grid or TIN theme can be accentuated, and different effects achieved, by altering the azimuth and altitude parameters. The azimuth is expressed in positive degrees from 0 to 360, measured clockwise from north. The altitude is expressed in positive degrees, with 0 degrees at the horizon and 90 degrees directly overhead.

The output grid theme from Compute Hillshade is automatically named "Hillshade 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 "hlshd" 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.


Converting raster and vector data sources

In the raster domain, certain functions, such as Map Query and Map Calculator, only work on grids. Because of this, you may find the need to convert images to grid data sources.

For layout, or to share data with people who don't have the ability to read grid themes, you may also need to convert grid data sources to feature data sources.

What type of conversion do you want to perform?

Feature theme to grid theme

Image theme to grid theme

Grid theme to polygon feature theme


Copying
To copy a data set

1	When a view is active, choose Manage Data Sources from the File menu.

2	Choose the type of source you want to copy from the Source Types dropdown.

3	Choose the data set to copy.

4	Press the Copy button.

5	Navigate to the directory you want to copy the data set to.

6	In the To Name type-in box, enter the name to copy the data set to. Press OK.

The above procedure copies data sets. These steps do not copy themes within a view.


Create contours for an entire theme
To create contours for an entire theme

For a grid or TIN theme

1	Activate the grid or TIN theme from which to create the contours in a view or 3D scene.

2	From the Surface menu, choose Create Contours.

3	Enter the contour interval in the Contour interval type-in box.

4	Specify the contour value to start contours at in the Base contour type-in box. Contours will be created above and below the base contour. Press OK.

For a point or multipoint theme

1	Activate the point or multipoint theme from which to create the contours in a view or 3D scene.

2	From the Surface menu, choose Create Contours.

3	If the view's analysis properties haven't been set to a specific value, or if the points were activated in a 3D scene, then you'll be prompted to set the extent and cell size for the output grid theme. Do so in the Surface 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	Specify the interpolation parameters necessary to create the temporary surface that contours will be created from, and press OK. For more information on setting the interpolation parameters using the Interpolate Surface dialog, see Interpolate Surface (Dialog box).

5	Enter the contour interval in the Contour interval type-in box.

6	Specify the contour value to start contours at in the Base contour type-in box. Contours will be created above and below the base contour. Press OK.

Smaller contour intervals create more contours. The optimum contour interval is a matter of the elevation change in the input grid or TIN theme, the amount of area covered by the theme, the analysis to follow, and the desired aesthetics of the output line theme.

Create Contours works off of the selected set if the active theme 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.

Create Contours produces an output line theme. The shapefile associated with the output theme is written to the project's working directory, with the name "ctourX.shp" with X denoting 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.


Creating surfaces from point samples
To create surfaces from point samples

1	Activate a point or multipoint theme.

2	From the Surface menu, choose Interpolate Grid.

3	If the 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 Interpolate Surface dialog, choose an interpolation method from the Method dropdown list, IDW or Spline.

5	Choose the field containing the values to be used in the interpolation from the Z Value Field dropdown list. The value of Z Value Field for a multipoint feature is used for each point in that feature.

6	Specify the parameters for the chosen interpolation method in parameter type-in boxes. With IDW, you must specify whether it will use Nearest Neighbors or a Fixed Radius in the interpolation. If you choose Nearest Neighbors, enter the number of neighbors (input points). If you choose Fixed Radius, enter the radius to search for points. Specify a power, and choose a barrier theme. If you choose the Spline interpolation method from the Method dropdown list, enter a weight factor, specify the number of points to use per region, and choose Regularized or Tension. Press OK.

Visiting every location in a study area to measure the height, magnitude, or concentration of a phenomenon is usually difficult or expensive. Instead, select strategically dispersed sample input point locations, and use Interpolate Surface to assign an estimated value to all other locations. Input points can be either randomly or regularly spaced points containing height, concentration, or magnitude measurements.

The resulting grid theme is the best estimate of what the quantity is on the actual surface for each location. The surface interpolators make certain assumptions about how to determine the best estimated values. Based on the phenomena the values represent and on how the sample points are distributed, different interpolators will produce better estimates relative to the actual values. No matter which interpolator is selected, the more input points and the greater their distribution, the more reliable the results.

The Inverse Distance Weighted (IDW) interpolator assumes that each input point has a local influence that diminishes with distance. It weights the points closer to the processing cell greater than those farther away. A specified number of points, or optionally all points within a specified radius, can be used to determine the output value for each location. Use it, for example, to interpolate a surface of consumer purchasing. More distant locations have less influence, because people are more likely to shop closer to home. The power parameter in the IDW interpolation controls the significance of the surrounding points upon the interpolated value. A higher power results in less influence from distant points. Each line in a barrier input line theme is used as a break that limits the search for input sample points. A line can represent a cliff, ridge, or some other interruption in a landscape. A choice of No Barriers will use all points specified in the No. of Neighbors or within the identified radius.

The Spline interpolator is a general purpose interpolation method that fits a minimum-curvature surface through the input points. Conceptually, it is like bending a sheet of rubber to pass through the points, while minimizing the total curvature of the surface. It fits a mathematical function to a specified number of nearest input points, while passing through the sample points. This method is best for gently varying surfaces such as elevation, water table heights, or pollution concentrations. It is not appropriate if there are large changes in the surface within a short horizontal distance, because it can overshoot estimated values. The Regularized method yields a smooth surface. The Tension method tunes the stiffness of the surface according to the character of the modeled phenomenon. When you choose Regularized, the weight parameter defines the weight of the third derivatives of the surface in the curvature minimization expression. If you choose Tension, the weight parameter defines the weight of tension. The number of points parameter identifies the number of points per region used for local approximation.

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

The output grid theme from Interpolate Surface is automatically named "Surface 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 "sface" 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.


Deleting
To delete a data set

1	When a view is active, choose Manage Data Sources from the File menu.

2	Choose the type of source you want to delete from the Source Types dropdown.

3	Choose the data sets to delete. To select more than one data set hold the shift key on the keyboard down while choosing data sets.

4	Press the Delete button.

If a data set is being used in the open project, you won't be able to delete the data set. However, you will be able to delete data sets that are part of unopen projects without any warning.


Deriving aspect from a surface
To derive aspect from a surface

1	Activate the grid or TIN theme from which to derive aspect in a view or 3D scene.

2	From the Surface menu, choose Derive Aspect.

3	If the input theme is a TIN, specify the output extent in the Output Grid Extent dropdown list, the cell size in the Output Grid Cell Size Input field, and the number of rows and columns in the Number of Rows and Number of Columns input fields on the Output Grid Specification dialog. Press OK.

Derive Aspect identifies the steepest down-slope direction from each cell to its neighbors. The values of the output grid theme represent the compass direction of the aspect; 0 is true north, a 90 degree aspect is to the east, and so forth.

Cells in the input grid, or faces of input TIN theme of zero slope (flat) are assigned an aspect of -1. If any neighborhood cell surrounding the processing cell are No Data, they are assigned the value of the processing cell, then the aspect is computed.

A legend representing the 8 cardinal directions is assigned to the output grid theme (e.g., east [67.5 - 112.5 degrees], southeast [112.5 - 157.5]).

The output grid theme from Derive Aspect is automatically named "Aspect 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 "aspct" 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.


Deriving data from surfaces
Analyzing surfaces

Performs a specified calculation that results in different representations of a surface or that derives patterns not readily apparent in the original surface, using a continuous grid or TIN theme. With surface-analysis operations, you can derive additional information by producing new data and identifying patterns in existing surfaces.

What type of data do you want to derive from your surface?

Slope

Aspect

Hillshade


Deriving slope from a surface
To derive slope from a surface

1	Activate the grid or TIN theme on which to derive slope.

2	From the Surface menu, choose Derive Slope.

3	If the input theme is a TIN, specify the output extent in the Output Grid Extent dropdown list, the cell size in the Output Grid Cell Size Input field, and the number of rows and columns in the Number of Rows and Number of Columns input fields on the Output Grid Specification dialog. Press OK.

Derive Slope identifies the slope, or maximum rate of change, from each cell to its neighbors. The output slope grid theme represents the degree of slope (e.g., 10 degree slope) for each cell location.

The output grid theme from Derive Slope is automatically named "Slope 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 "slope" 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.


Displaying a grid theme

When grid themes are displayed, each cell is filled with a color. Cells contain values and values are mapped to colors through a legend. Legends can be classified so that each cell value is displayed with a unique color or groups of values given the same color. Cells are always filled with a solid pattern and this pattern can not be changed.

What do you want to know about displaying a grid theme?

Changing the colors used to display cell values

Choosing an appropriate legend type

Grouping cell values into categories: Classifying your data

Altering brightness of a grid theme


Error in reading STA table

The above error is the result of a corrupt info directory in the directory you are trying to write a new grid data set to. Corrupt info directories are caused by deleting, renaming, and copying grid data sets using the computers file management tools. You should always use Source Manager provided with ArcView to delete, rename, and copy grid data sets. The Source Manager is accessed from the View’s File menu by choosing Manage Data Sources.

  Related topics


Examining the cell values in a grid theme

Each cell in a grid theme has a value which represents the feature or characteristic located at that geographic position. A cell can contain more than just the attribute that gives it its value. You can add attributes to each value through its table. Cells with the same value must have the same attributes that you want to represent in the table. If two cells have the same value for one attribute but different values for another attribute, then these attributes must be contained in two different grid themes.

There are several ways to examine the cell values of a grid theme. You can identify the value of a single cell or display all cells that contain the same attributes. If your grid theme represents a continuous surface you can view a line of constant value from a graphic pick.

How do you want to examine the cell values of your grid theme?

Show all cells that have a specified attribute

Show the value of a specified cell

Trace the contour passing through a selected point


Exporting grid data sets to generic raster files

You may need to use grids with another cell-based model or raster system that doesn't support the ESRI grid data set. Grids can be exported to two generic raster file formats: ASCII and binary.

What do you want to know about exporting?

How to export

The ASCII raster file format

The binary raster file format


Feature theme to grid theme
To convert feature themes to grid themes

1	Click on the feature themes you want to convert to grid themes.

2	From the Theme menu, choose Convert to Grid.

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 Conversion Extent 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 Conversion Field dialog, choose a field in the feature theme that will be used to give values to the cells in the output grid theme. Press OK.

5	Provide a name and directory for the output grid data set, then press OK. Grid data set names cannot be longer than 14 characters and cannot contain a "." or space.

6	If the conversion field was a string or integer field, then you can choose whether or not to add all the attributes of the feature theme to the table of the output grid theme.

7	Choose whether or not to add the new grid theme to the view.

Start over with step 2 for each feature theme activated.

Any type of feature theme created form any type of source file can be converted to a grid theme. It doesn’t matter if the source data for a feature theme comes from a CAD drawing, ARC/INFO coverage, or shapefile; it can be converted to a grid theme. If you wish to convert a data base theme to a grid theme, you must first convert it to a shapefile with Convert to Shapefile in the Theme menu.

Only the selected features in a theme will be converted to the output grid theme. If the theme does not contain a selected set, then all features will be converted to the output grid theme.

When you convert polygons, cells are given the value of the polygon found at the center of each cell. When you convert lines, cells are given the value of the line that intersects each cell. Cells that are not intersected by a line are given the value of No Data. When you convert points, cells are given the value of the points found within each cell. Cells that don't contain a point are given the value of No Data. If more than one line or point is found in a cell, then the cell is arbitrarily given the value of one of the lines or points. If this is a problem, use a smaller cell size during conversion. If you have the Spatial Analyst then Neighborhood Statistics in the Analysis menu can be used to give you more control on which value is given to a cell.

You can convert feature themes using both string and numeric fields. If you use a string field, then each unique string in the feature theme is assigned a unique value in the output grid theme. A field named S_Value will be added to the table of the output grid theme to hold the original string value from the feature theme.


Grid theme to polygon theme
To convert an integer grid theme to a polygon feature theme

1	Click on the integer grid themes you want to convert to polygon feature themes, to make them active.

2	From the Theme menu, choose Convert to Shapefile.

3	Provide an output name and directory for the output shapefile created during conversion. Press OK.

4	Choose whether or not to add the new polygon feature theme to the view.

Start over with step 2 for each grid theme you activated.

Only the selected cells of an integer grid theme will be converted to polygons. If the integer grid theme does not contain selected cells, then all the cells will be converted to polygons.

The output polygon feature theme will contain a field called Gridcode. This field will hold the value of the cells that created the polygon in the integer grid theme.

The polygons in the output feature theme are smoothed in such a way that makes them appear smooth but still retains the positional accuracy of the data. Converting the output feature theme back to an integer grid theme, with Convert to Grid in the Theme menu, with the original cell size and extent, will demonstrate that the positional accuracy is preserved by making an exact copy of the original integer grid theme.


Grouping cell values into categories
Grouping cell values into categories: Classifying your data

The purpose of grouping cell values is to both explore your data and make it easier to understand. The cell values of a grid theme can be grouped for display in one of five ways:

 Equal Area - Groups cells so there is an equal number of cells in each of the output classes. Use this to display integer grid themes that contain a continuous variable, such as elevation, when you wish to see more contrast between cell values.

 Equal Interval - Groups cells by dividing the range of cell values into equal sized sub-ranges.

 Natural Breaks - Groups cells by identifying 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 - Groups cells so there is an equal number of features in each of the output classes. For grid themes Quantile and Equal Area classifications are exactly the same.

 Standard Deviation - Groups cells by finding the mean cell value and then placing 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 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.").

Floating point grid themes only allow the Equal Interval and Standard Deviation classification methods, because not all of their values are easily available to perform other classification methods.


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

For most operations of the Spatial and 3D Analysts, there's a Stop button to the right of the progress bar at the bottom of the ArcView window. Press it to stop the operation that is currently running.

If you are working in the Spatial Analyst and find that an operation is taking a long time to process, press the Stop button and check the analysis properties for the view you are working with. The analysis cell size might not be appropriate for the analysis extent set for that view, resulting in an output that is much larger than desired. Also check that the inputs to an operation are in the same coordinate system and have overlapping coordinates, if the analysis extent is set to Union of Inputs.


How do theme and data set names get generated
How do theme and data set names get generated?

Because an output may be temporary, the operations in the Analysis menu won't prompt you for the name of an output theme or data set. This allows you to perform analysis without having to specify a name until you're sure you've got the answer you want.

The name generated for output themes indicates the operation that created it. Examples are "Distance to Roads.shp" for Find Distance, "Contours from Elevgrd" for Create Contours, and "Reclass of Landuse" for Reclassify. Use Properties in the Theme menu to change the name of a theme.

The data set associated with the output theme is written to the project's working directory, with the name consisting of 3 to 5 characters representing the operation run 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. A grid data set associated with the output theme created with an operation in the Analysis or Surface menu 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.

The following is a list of operations in the Surface menu (used by both the 3D and/or Spatial Analysts) and the 3 to 5 character roots used to name data sets resulting from the operations

 Interpolate Grid - sface

 Derive Slope - slope

 Derive Aspect - aspct

 Compute Hillshade - hlshd

 Create Contours - ctour (output is a shapefile with a file extension of .shp)

 Calculate Viewshed -vwshd

 Cut Fill - cutfl

The following is a list of the operations in the Analysis menu (used only by the Spatial Analyst) and the 3 to 5 character roots used to name data sets resulting from the operations

 Find Distance - dist

 Assign Proximity - prox

 Calculate Density - denst

 Cell Statistics - major (majority), max (maximum), mean (mean), med (median), min (minimum), minor (minority), range (range), stdev (standard deviation), sum (sum), var (# of unique occurrences)

 Summarize Zones - zstat (output is a dBASE file with a file extension of .dbf)

 Tabulate Areas - tarea (output is a dBASE file with a file extension of .dbf)

 Map Query - query

 Map Calculator - calc

 Neighborhood Statistics - nbmjr (majority), nbmax (maximum), nbmen (mean), nbmed (median), nbmin (minimum), nbmnr (minority), nbrng (range), nbstd (standard deviation), nbsum (sum), nbvar (variety)

 Reclassify - rclss


How projections affect analysis

If you set a projection on a view, then your vector feature theme data (points, lines, polygons) must be stored in decimal degrees. The data is projected on the fly and displayed in the new coordinate system. Raster data, such as grids and images, do not work in the same manner, because projecting raster data is time consuming. TINs, while vector, do not get projected either because the result may yield an invalid triangulation. Grids, images, and TINs are assumed to be in the correct projection already and are not transformed. This affects the way feature theme data and grids, images, and TINs are treated during analysis. Below are some suggestions for integrated analysis of both projected and non-projected data along with the implications of that analysis.

When your feature theme data is in decimal degrees and your grids, images, or TINs are in projected coordinates

The projection for the view must be set to the projection of the raster or TIN data. Your feature theme data is projected to the coordinates your raster or TIN data is already in. This will allow the data to align and you are able to perform integrated analysis. Any vector feature theme data created during analysis is created in decimal degrees. Any raster or TIN data created during analysis is created with coordinates in the projected space.

When both your feature theme data and raster or TIN data are in the same projected coordinates

Do not set a projection for the view in which analysis is performed. Your feature theme, raster, and TIN data will align in the view. Any data that is created during analysis is created with coordinates in the projected space.

When all your feature theme, raster, and TIN data is in decimal degrees

Do not set a projection for the view in which analysis is performed. If a projection is set then your vector feature theme data is projected, but your raster and TIN data is not. This will cause the data to appear in two separate places, not allowing you to perform integrated analysis. With the projection turned off, any feature theme, raster, or TIN data created during analysis is created in decimal degrees. Be aware that grids or TINs intended for use with many surface analysis functions should NOT be in decimal degrees. Algorithms in these functions assume a Cartesian coordinate system.


How to export
To export a grid data set to a generic raster file

1	Activate a view.

2	From the File menu, choose Export Data Source.

3	Select the type of raster file to export to. You can choose between ASCII and Binary. Press OK.

4	With the next dialog, navigate to the directory that holds the grid data sets you want to export. Select some grid data sets. Press OK. Each grid data set will be exported to a separate raster file.

5	Provide a name and directory to place each of the new raster files created, and press OK. The Binary raster file format creates two files. The first, the file that will hold the data, will be the file you provide a name for. There will also be an ASCII header file with the same name, but with a .hdr file extension. If your grid data set contains projection information, then a projection file is also created with a .prj file extension.


How to import
To import data from generic raster files

1	Activate a view.

2	From the File menu, choose Import Data Source.

3	Select the type of raster file to import. You can choose between ASCII, Binary, USGS DEM, and US DMA DTED. Press OK.

4	With the next dialog, navigate to the directory that holds the raster files you want to import. Select some files to import. Press OK. A grid data set will be created for each file you select.

5	Provide a name and directory to place each of the new grid data sets created. Grid data set names must be less than 14 characters long and cannot contain a "." or space. Press OK.

6	If importing from ASCII files, choose whether or not to create a grid data set with integer or floating point values.

After the raster files have been imported to grid data sets, you can add the new grid data sets to a view as themes with the Add Theme button [image].


Image theme to grid theme
To convert image themes to grid themes

For an image theme with a single band

1	Activate the image themes that you want to convert to grid themes by clicking on them.

2	From the Theme menu, choose Convert to Grid.

3	Provide a name and directory for the output grid data set, then press OK. Grid data set names cannot be longer than 14 characters and cannot contain a "." or space.

4	Choose whether or not to add the new grid theme to the view.

For an image theme with multiple bands

1	Activate the image themes that you want to convert to grid themes by clicking on them.

2	From the Theme menu, choose Convert to Grid.

3	You are prompted if you want to convert all bands or not. If Yes then goto step 5. If No then continue to next step

4	Select the band you want to convert.

5	Provide a name and directory for the output grid data set, then press OK. This will be repeated for every band if you selected to convert all bands. Grid data set names cannot be longer than 14 characters and cannot contain a "." or space.

6	Choose whether or not to add the new grid theme to the view. This will be repeated for every if you selected to convert all bands.

Image themes created from image catalogs or grid data sets cannot be converted to grid themes. You also cannot convert an image theme whose data source has rotation parameters in its world file.

The conversion of image themes to grid themes is merely a change in file type. The output grid theme will have the same extent, cell size, and cell values as the original image theme. The analysis environment settings for the view are ignored.

If the image theme’s data source has a colormap, then this colormap is written to a file to be used with the new grid data set. The colormap is given the same name as the output grid data set, with a .clr file extension appended to it. If you add this grid data set to a view as an image theme, then this colormap file is used to display the data set.


Importing data from generic raster files

You may have raster data from other cell-based models or raster systems that you want to use. If this data is not in a format supported by image or grid themes, you will have to import it to a grid data set instead of converting between theme types or using it directly. The following raster formats can be imported: ASCII, binary, DTED, and USGS DEM.

For information on supported image formats, see Supported image formats .

What do you want to know about importing?

How to import

The ASCII raster file format

The binary raster file format

The USGS DEM raster file format

The US DMA DTED raster file format


I only see 1 or 2 colors when the legend has more
Why you only see one or two colors when the legend has more

You probably have extreme high or low cell values that are not similar to the majority of the cell values in your grid theme. Grid themes with a large range of cell values are displayed with an equal interval classification by default. If you have extremely high or low cell values, most cell values fall into one or two class, causing the grid theme to be displayed with only one or two colors.

For an integer grid theme, you can change the classification method of the legend to equal area. This will force an equal number of cells into each class of the legend, resulting in more contrast on the display. For more information on changing the classification of a theme, see Setting a classification.

The equal area classification method is not available for floating point grid themes. For a floating point grid theme, you can change the high or low cell values to No Data, to another value closer to the rest of the cell values, or convert the theme to an integer grid theme. If you have the Spatial Analyst you can use Reclassify in the Analysis menu to reclassify the cell values.

If you have the Spatial Analyst you can also use the Int button [image] in the Map Calculator to convert a grid theme's floating point cell values to integer values. The Map Calculator dialog can be brought up with Map Calculator in the Analysis menu. After the grid theme is converted to an integer grid theme, you can use the equal area classification method.


Mapping contours

Contouring produces an output line theme from an input grid or TIN theme. The value of each line represents all contiguous locations with the same height, magnitude, or concentration of whatever the values on the input grid or TIN theme represent. The output theme will contain a field called Contour in its attribute table which lists the value of each contour.

For grid themes the function does not connect cell centers; it interpolates a line that represents locations with the same magnitude. Rarely will the line pass through the original cell centers. Since the lines are smoothed, a realistic representation of the surface contours is produced.

For TIN themes the function interpolates a series of lines through the network of triangles, examining every triangle edge to see if a contour passes through it. Linear interpolation between the edge endpoints is used to calculate a contour’s position along the edge.

You can create an individual contour line by clicking the Contour tool [image], and then selecting a location in the view. The function traces the contour of the value that the chosen point represents.

How do you want to map contours?

Create contours for an entire theme

Trace the contour passing through a selected point


Performing viewshed analysis

1	Activate a grid or TIN theme that will serve as the elevation surface on which the viewshed will be determined in a view or 3D scene.

2	Also, activate a point or line theme, which will be used to supply the observation points.

3	Choose the Calculate Viewshed option under the Surface menu.

4	If the input elevation surface is a TIN, specify the output grid extent on the Output Grid Extent dropdown list, the cell size in the Output Grid Cell Size input field, and the number of rows and columns in the Number of Rows and Number of Columns input fields on the Output Grid Specification dialog. Press OK.

Viewshed analysis indicates not only what areas of a surface can be seen by one or more observers, but also, for any visible position, how many observers can see the position. The result is a grid theme with visibility attributes assigned to every cell. The assigned values are the number of observation points from which a particular location can be seen.


Frequently asked questions about grid data sets
Questions about Grid Data Sets

What do you need help with?

Where did my data set go?

The data set for my theme changed

Which data set belongs with which theme?

Where do my data sets get written?

Error in reading STA table


Frequently asked questions about grid themes
Questions about Grid Themes

What do you need help with?

Why doesn't my vector and raster data align?

Why can't I display a table for my theme?

Why can't I make graphical selections on my theme?

Why doesn't my theme have a legend?

The data set for my theme changed

Which data set belongs with which theme?

Why you only see one or two colors when the legend has more


Renaming
To rename a data set

1	When a view is active, choose Manage Data Sources from the File menu.

2	Choose the type of source you want to rename from the Source Types dropdown.

3	Choose the data set you want to rename.

4	Press the Rename button.

5	Navigate to the directory you want to move the data set to.

6	In the To Name type-in box, enter the name to rename the data set. Press OK.

The identified data sets are only renamed, they are not copied. You cannot rename a data set that is being used in the open project. When a data set is renamed and is part of an unopened project, you'll be queried, when the unopened project is opened, as to where the renamed data set is now located and named.


Saving
To save a grid data set

All grid data sets underlying the grid themes resulting from the operations in the Analysis and Surface menu are temporary. If you delete one of these grid themes, the underlying data set is deleted. To save one of these grid data sets so that it can be accessible to other users or for other projects, use the following steps:

1	Activate the grid theme from which to save the underlying data set.

2	From the Theme menu, choose Save Data Set.

3	Navigate to the directory in which to save the data set.

4	Enter the name of the grid data set in the Grid Name type-in box. Press OK.

When you save the grid data set to another directory and under a different name, the grid theme in the view is automatically updated. Saving the project will also change all temporary grid data sets in the project to permanent.

Use Properties in the Theme menu to check the status of the underlying grid data set of a grid theme.

Use Manage Data Sources from the File menu to delete any permanent grid data sets.


The data set for my theme changed

You may find that the data set for a grid theme has changed when you reopen a project. Someone may have deleted the data set associated with that grid theme. Because the Spatial and 3D Analysts write data sets they create into the project's working directory with temporary names, another data set with the same name as the original data set may have been created. If a data set was not created with the same name, the project would have gone into project repair when it was opened, as ArcView couldn't locate the data set. For more information on how the Spatial and 3D Analysts name output themes and data sets, see How do theme and data set names get generated?.


The value of a specified cell
To show the value of a specified cell in a grid theme

1	Click on the grid themes you want to identify cell values for, to make them active.

2	Click on the Identify tool [image].

3	Click on a cell in the view.

The Identify Results dialog will display. On the left, it shows the names of the active grid themes and the x and y coordinates of the center of the cell. On the right, it shows the cell value and any other attributes for the cell. If you have more than one active theme, select a different item on the left side of the dialog to change the information shown on the right.


Trace the contour passing through a selected point
To trace the contour passing through a selected point

1	In a view, click on a grid or TIN theme to make it active. Use only grid themes representing a continuous attribute, such as elevation or density.

2	Click on the Contour tool [image].

3	Click on a location on the grid or TIN theme to see its contour.

The contour is drawn on the view as a graphic line. Its value is displayed on the left side of the status bar. The contour graphic lines are added to the graphics list for the grid or TIN theme that they were created from. They will only be displayed when this theme is displayed. The current line symbol is used to draw the graphic contour lines. You can change the line symbol used to draw the graphic contour lines by first making sure that no graphics are selected and then choosing Show Symbol Window in the Window menu.

You can also put the contour lines directly into another theme and write the contour values to the table of that theme.

To put contour lines directly into a new theme

1	From the View menu, choose New Theme.

2	Choose Line as the feature type and press OK.

3	Provide the directory and file name for the new theme, and press OK.

4	Click on the grid or TIN theme you want to trace contours from, to make it active.

5	Click on the Contour tool [image].

6	Click on the location on the grid or TIN theme that you want to create a contour for.

The contour is placed into the new theme. A field is added to the new theme with the value of the contour. To stop placing contours into the new theme, click on the theme to make it active. From the Theme menu, choose Stop Editing. When prompted, press Yes to save edits.


What is a grid data set
What is a grid data set?

The Spatial and 3D Analysts have the ability to create grid data sets and work with them. A grid data set is stored in a directory called a workspace. Each grid data set is stored as a separate directory with associated tables and files that contain specific information about the grid. Each grid data set also stores some files in an INFO directory found in the workspace. All output grid data sets are created in the project's working directory. By default this is the user’s home directory and can be set using the Project Properties dialog or by choosing Set Working Directory from the view windows File menu.

Do not use your computer's file system commands with grid data sets

Because each grid data set stores files in the INFO directory, you cannot rename, copy, or delete them with the computer's file system. Rename, copy, or delete grid data sets with the Data Source Manager supplied with Spatial and 3D Analysts. You can access the Manager Data Sources dialog from the File menu when a view is active. However, you can move entire workspaces with the computer's file system with no problems.

Temporary vs. permanent grid data sets

Grids created as a result of performing analysis are stored as temporary data sets. They are deleted when the corresponding grid theme is deleted from the view, or if you exit ArcView without saving the project. All grid data sets become permanent when you save the project, or if the theme is active and you use Save Data Set from the Theme menu. Once a grid data set is made permanent, it will not be deleted when the grid theme or project is deleted.


What is a grid theme
What is a grid theme?

A grid theme represents a geographic layer where space is partitioned into square cells in a view. Each cell stores a numeric data value that conveys information about the geographic layer it represents.

Each grid theme has its own legend display in the view's Table of Contents. A grid theme’s legend specifies what color is given to its cell values. This controls how the grid theme is displayed in the view.

Depending on the information it represents, a grid theme may be created out of either integer or floating point values. A grid theme created out of integer values can have an associated table that summarizes the attributes it contains. Cells that have the same value will have the same attributes. Grid themes created out of floating point values will not have associated tables. Since it is likely with floating point data that no two cells will have the same value, there is no need to summarize the values individually in an associated table.

The data used to create a grid theme can be on a local disk or accessed across a network. A grid theme merely points to the geographic data it represents; it does not contain the data itself.


Where did my data set go
Where did my data set go?

Grid data sets created from analysis operations are temporary. These temporary data sets are created in the project’s working directory. This would be the first place you should look for your missing data set. You can find out where your projects working directory is by clicking on the project window to activate it and selecting Properties in the Project menu. If you can't find your grid data set in this directory, then it could have been deleted. Data sets are deleted for one of two reasons:

 If you delete a grid theme created from an analysis step, the associated grid data set will also be deleted if it's tagged as temporary.

 If you close a project without saving it, all grid themes created through analysis after the project was opened are deleted, causing the associated grid data sets tagged as temporary also to be deleted.

Temporary grid data sets can be made permanent, see Saving.

Grid data sets created by Convert to Grid are permanent.


Where do my data sets get written
Where do my data sets get written?

Data sets created with operations in the Analysis and Surface menu are written to the project's working directory using a temporary name. Use Properties in the Project menu to change the project's working directory or choose Set Working Directory in the File menu when a view is active. For more information on how the Spatial and 3D Analysts name output data sets, see How do theme and data set names get generated?.


Which data set belongs with which theme
Which data set belongs with which theme?

Because an output may be temporary, the operations in the Analysis and Surface menu won't prompt you for the name of an output theme or data set. This allows you to perform analysis without having to specify a name until you are sure you've got the answer you want. Use Properties in the Theme menu to find out which data set belongs with which theme. For more information on how the Spatial and 3D Analysts name output themes and data sets, see How do theme and data set names get generated?.


Why cant I display a table for my grid theme
Why can’t I display a table for my grid theme?

Only integer grid themes can have an associated table. Since every cell in a floating point grid theme could have a different value, the cell values are not summarized in a table. Integer grid themes with ranges of values over 100,000 or with over 500 unique values will also not have an associated table, by default. Use Properties in the Theme menu to find out if a grid theme is integer or floating point.


Why cant I make graphical selections on my grid theme
Why can’t I make graphical selections on my grid theme?

If you selected a cell on the view, all cells with that same value, whether they were within the area defined to make the selection or not, would be selected. To prevent this confusion of cells highlighting outside the selection area, the Spatial and 3D Analysts don't allow graphical selections on a grid theme. You can make selections on an integer grid theme from its associated table. For more information on how to select cells in a grid theme, see Show me all cells that have a specified attribute.


Why doesnt my grid theme have a legend
Why doesn’t my grid theme have a legend?

A grid data set can be added to a view as a grid or image theme. If it's added to a view as an image theme, then it will not have a legend displayed in the table of contents for the view. If you want a legend displayed in the table of contents, then add the grid data set as a grid theme.


Why doesnt my vector and raster data align in the view
Why doesn't my vector and raster data align in the view?

Grid themes are displayed using the coordinates found in the data set, regardless of the projection set for a view. Your feature themes and grid themes must be in the same coordinate system to display them together without a projection set on a view. If a projection is set for a view, then your feature themes must be in decimal degrees and your grid themes must be in the projection set for the view for them to be displayed together. For more information on how the Spatial and 3D Analysts handle projections, see How projections affect analysis.