Spatial Analyst—Module 3 Curvature Model

Spatial Analyst—Module 3: Curvature Model

If you encounter problems with the file provided on this page, please contact Soil Survey at 406-587-6818.

The information on this page is also available in Acrobat Reader format. Once you have saved the file to a local drive, open Acrobat Reader then open the saved file on your local drive.

Module 3: Curvature Model (PDF; 1.8 MB)

Objectives and Tasks

Intersect a Curvature Layer with a Soil Polygon Layer
  1. Review Slope Curvature Model
  2. Create a Standard Hillshade
  3. Run Curvature Model
  4. Add\Symbolize\Evaluate Curvature Shapefile
  5. Intersect Curvature Shapefile and Soil Polygon Layer
  6. Export Soil\Curvature Intersect Data Table
  7. Summarize Slope Shape by Soil Map Units

For the Curvature Model to work properly, the directory structure listed below must exist on your computer.


Review Slope Gradient Model

  • Layers & data derived from Curvature Analysis provides users with a picture of the overall slope shape—what areas are convex, concave, and linear.
  • This information allows us to separate erosional and depositional surfaces; this is significant for soil genesis.
  • The layers created from the Curvature Model can be used to assist in premapping or to adjust existing soil lines.
  • The intersection of curvature shapefiles and soil polygons provides statistical information on slope shape for each map unit. This could help determine map unit composition.
  • The output from the Curvature Model is a grid. Each cell value is a composite of 2 values that represent slope shapes that are the perpendicular (profile) and parallel (planar) to the slope. The composite grid delineates the 9 different slope shapes.
  • The first number represents values from the profile grid (up slope); the second number represents the values from the planar grid (across slope).
    • Profile grid (upslope): 1 = Convex; 3 = Linear; 5 = Concave
    • Planar grid (across slope): 1 = Concave; 3 = Linear; 5 = Convex

Create a Standard Hillshade

Open the “sa_training” ArcMap project, turn off all layers, and collapse all legends.

Hint: To collapse or expand all legends
  1. Hold the ctrl-key and click on one of the legend boxes
  2. To turn on or off all layers, hold the ctrl-key and click on one of the layer boxes
To create a hillshade from the Spatial Analyst Toolbar
  1. Click on Spatial Analyst then Surface then Analysis then Hillshade
In the Hillshade dialog box
  1. Set the Input surface to your DEM; e.g., “bv83_clip”
  2. Set the Z factor to 2 (the Z factor increases the vertical exaggeration for 3D effect)
  3. Accept all other default values
  4. Click OK to create
  • A magnification of the hillshade with contour lines applied reveals the complexity of the slope shapes.
  • The curvature model can provide acres and percent composition of the different slope shapes.
  • For example, if “Alpha” soil occurs on convex-convex positions in this area, the curvature model can calculate the percent composition of that slope shape.

Run Curvature Model

  • The curvature model creates a shapefile and a raster of slope shapes derived from an elevation grid (DEM).
  • For this model to function, the following directory structure must exist: "c:\home\data\spatial_analyst\shapefiles."
  • A slope shape raster ("curve") will be created in the "c:\home\data\spatial_anaylyst\shapefiles" directory.
  • The output grid and shapefile will have 9 different values.
  • These values are indicative of the slope shape for that cell.
  • These values are:
    • 11 = convex profile, concave planar
    • 13 = convex profile, linear planar
    • 15 = convex profile, convex planar
    • 31 = linear profile, concave planar
    • 33 = linear profile, linear planar
    • 35 = linear profile, convex planar
    • 51 = concave profile, concave planar
    • 53 = concave profile, linear planar
    • 55 = concave profile, convex planar
  1. If Toolbox is not open, click on the Toolbox Icon
  2. In ArcToolbox, click on Soils -- Spatial Analyst Tools then Slope/Curvature Models then Curvature
  3. In the Curvature dialog box, select the Input Raster (DEM) by clicking on the down arrow and selecting your DEM; e.g., “bv83_clip”
  4. An explanation of the output rasters and shapefile is described in Help
  5. Click OK to create a shapefile and rasters of profile, planar, and composite curves
  6. A slope shape shapefile (“slope_shape”) is created in c:\home\data\spatial_analyst\shapefiles
  7. A raster slope shape (“curve”) is created in c:\home\data\curvature
  8. For this model to work, create the same directory structure on your computer

Add\Symbolize\Evaluate Curvature Shapefile

To add the layer created by the Curvature Model
  1. Click on the Add Data icon
  2. Navigate to c:\home\data\spatial_analyst\shapefiles
  3. Select “slope_shape”

To symbolize the “slope_shape” shapefile
  1. In the Data Frame window, double click on “slope_shape” to open Layer Properties box
  2. Click on the Symbology tab
In the Layers Properties window under the Symbology tab
  1. Click on Categories then Unique values
  2. Select “Slp_shape” for the Value Field
  3. Uncheck the “all other values” box
  4. Click on the “Add All Values” button
  5. Click OK

Intersect Curvature Shapefile and Soil Polygon Layer

In ArcToolbox, click on Soils -- Spatial Analyst Tools then Soil Intersect then Slopeshape-Mapunit Dissolve

This model intersects a slope shape shapefile with a soil polygon layer. The model then dissolves polygons based on inputs (“MUSYM” and “Slp_shape”).

If the output from this model is used in an Excel worksheet, the dissolve process is needed to reduce the number of records (Excel can only have up to 65,536 rows).

In the Slopeshape-Mapunit Dissolve dialog box
  1. Click on the Input Features dropdown arrow
  2. Add a soil polygon layer, e.g., “soil_clip”, and a slope shape shapefile, e.g., “slope_shape”
In the Dissolve Field window
  1. Check “Slp_shape” and “MUSYM;” this will aggregate data based on slope shape and map unit symbol.
  2. Click OK to begin process
  3. A shapefile named “slpshape_mapunit_dissolve” is created in c:\home\data\spatial_analyst\shapefiles

Export Soil\Curvature Intersect Data Table

  1. Click on the Add Data icon
  2. Add the layer created by the Slope-Mapunit Dissolve Model
  3. Navigate to c:\home\data\spatial_analyst\shapefiles
  4. Select “slpshape_mapunit_dissolve"
In the Data Frame window
  1. Right click on the “slpshape_mapunit_dissolve” layer
  2. Select Open Attribute Table
  3. Click on the Calculate Area/Acres icon
If the Acres field is empty or has zeros
  1. Click on the Options button and select Reload Cache
  2. To export your table, click on the Options button and select Export
  3. Browse to the c:\home\data\spatial_analyst\tables directory and name the file “soil_slpshape”
  4. Save the file to a “dBase Table”
  5. Click Save
  6. In the menus that follow, select OK to export and No to add the table to ArcMap

Summarize Slope Shape by Soil Map Units

In Microsoft Excel
  1. Click on File then Open
  2. In the window “Look in,” navigate to c:\home\data\spatial_analyst\tables
  3. In the window “Files of type,” select “dBase Files”
  4. Click on the “soil_slpshape” file and click on Open
To create a Pivot Table
  1. In the dropdown menu, select Pivot Table and PivotChart Report
  2. Click on Data
In the Pivot Table Wizard
  1. Check the radio button for Microsoft Office Excel list or database
  2. Check the radio button for Pivot Table
  3. Click on Finish

From the PivotTable Field List

  1. Drag and drop the “MUSYM” and “Slp_shape” fields into the “Drop Row Fields Here” box (make sure the MUSYM field is left of the Slp_shape field)
  2. Drag and drop the “Acres” field to the “Drop Data Items Here” box

The resulting table displays the number of acres by slope shape, for each map unit and lists the total acres by map unit.

To calculate the percent composition for each slope shape, by map unit
  1. double click on the Sum of Acres field
  2. Click on Options
  3. Under Show data as:, select “% of column”
  4. Click OK to finish

These values represent the percentage of total acres for a map unit slope shape. For example, “linear-linear” slope shapes in map unit 010A account for 1.89% of the total acres (1.89% of total acres, not map unit acres).
Also, 010A accounts for 2.18% of the total acres.

To view slope shape percentages for a single map unit
  1. Click on the down arrow next to MUSYM
  2. Uncheck the box next to (Show All)
  3. Next, place a check next to any single map unit and click OK
  • About 87% of 010A has a slope shape of “linear-linear.”
  • To view results for other map units, click on the down arrow, uncheck 010A, and place a check next to a different map unit.