Analytics

Suitability modeling workflow using ArcGIS Desktop—Lesson 3: Weighting and combining data

    In lessons 1 and 2, you derived and transformed criteria for the Habitat submodel onto a common scale. In this lesson, you will weight and combine the transformed criteria into a single surface depicting the suitability for the Habitat submodel. You will also weight and combine the three submodels (Habitat, Food, and Security) into the final suitability surface.

    This lesson is divided into three sections:

    1. Opening and editing the ModelBuilder model
    2. Using the Weighted Sum tool to weight and combine transformed criteria
    3. Using the Weighted Sum tool to weight and combine submodels

    ArcGIS Spatial Analyst extension is required for this analysis and you must ensure that it is enabled. See Enabling the Spatial Analyst extension.

    This lesson continues on the data that you downloaded in lesson 1. If you have not downloaded the data, see the first section in Lesson 1: Exploring and deriving data.

    Opening and editing the ModelBuilder model

    1. If the SuitabilityModeling map document was closed after lesson 2, reopen it by double-clicking the SuitabilityModeling.mxd file in the SuitabilityModeling folder.

      Browsing to SuitabilityModeling.mxd

    2. Open the SuitabilityModel model that you started building in lessons 1 and 2 by right-clicking the model and clicking Edit.

      Opening the SuitabilityModel ModelBuilder model

    Using the Weighted Sum tool to weight and combine transformed criteria

    The Weighted Sum tool will be used to combine the transformed criteria in the Habitat submodel into a single surface.

    1. The Weighted Sum tool requires Spatial Analyst. Turn on the extension by first clicking the Customize tab in the ArcMap taskbar. Choose the Extensions option from the drop-down list, and check the Spatial Analyst check box to turn it on.

      Browsing to the Extensions dialog box

      Checking the Spatial Analyst extension

    2. Click the ArcToolbox icon ArcToolbox on the Standard toolbar. Browse to the Weighted Sum tool in the Overlay toolset in the Spatial Analyst Tools toolbox.

      Browsing to the Weighted Sum tool

    3. Drag the Weighted Sum tool into the SuitabilityModel model and place it to the right of the transformed datasets.

      Adding the Weighted Sum tool to the ModelBuilder model.

    4. Using the Connect tool Connect in the ModelBuilder taskbar, connect the three transformed layers (Transformed_LandUse, Transformed_Streams, and Transformed_Slope) to the Weighted Sum tool. Choose the Input rasters option each time.

      Connecting the Transformed_LandUse, Transformed_DistanceStreams, and Transformed_Slope layers to the Weighted Sum tool as the Input rasters

    5. Double-click the Weighted Sum tool to open the dialog box. Enter the appropriate weights in the Weight column. Type HabitatSubmodel into the Output raster parameter. This dataset is automatically saved into the Output.gdb geodatabase. To summarize the input and output layers for the Weighted Sum tool, specify the parameters as follows:
      • Input rasters: Transformed_Landuse, Transformed_Slope, Transformed_Streams
      • Output raster: HabitatSubmodel
      • Weight: Transformed_Landuse (2), Transformed_Slope (1), Transformed_Streams (1)

      Weighted Sum tool dialog box with parameters specified

    6. Click OK to apply the changes and close the Weighted Sum tool's dialog box.
    7. Right-click the Weighted Sum tool and click Run to execute the tool.

      Running the Weighted Sum tool within the model

    8. Right-click the output HabitatSubmodel layer (green) and click Add To Display to add the output HabitatSubmodel layer to the map document.

      Adding the results from Weighted Sum to the display

    9. Choose a red-to-green color ramp for the HabitatSubmodel layer to help portray each location's suitability related to habitat. Double-click the HabitatSubmodel layer in the table of contents and change the Color Scheme under the Symbology tab. To ensure the statistics on the raster are calculated, first select the Classified option from the left panel and if asked, build the histogram by clicking Yes. Then select the Stretched option from the left panel before choosing a red-to-green color ramp from the drop-down options. Click OK once the color ramp has been selected to apply it to the layer.

      Changing the symbology of the resulting weighted layer

    10. Explore suitability surface values within the HabitatSubmodel layer by clicking the map in different locations using the Identify tool Identify, found on the Tools toolbar.

      Habitat submodel suitability layer

    Using the Weighted Sum tool to weight and combine submodels

    1. Using the ArcCatalog window to the right of the map display, from the Data.gdb file within the SuitabilityModeling directory, add the FoodSubmodel and SecuritySubmodel layers to the table of contents by dragging the layers from Data.gdb into the table of contents.

      Adding the FoodSubmodel and SecuritySubmodel layers to the table of contents

    2. As you just did for the HabitatSubmodel, choose a red-to-green color ramp for the FoodSubmodel and SecuritySubmodel layers to help portray each location's suitability for each submodel. Double-click each layer in the table of contents and change the Color Scheme under the Symbology tab. Select the Stretched option from the left panel before choosing a red-to-green color ramp from the drop-down options. Click OK once the color ramp has been selected to apply it to the layer.
    3. Explore suitability surface values within the SecuritySubmodel layer by clicking the map in different locations using the Identify tool Identify, found on the Tools toolbar.

      SecuritySubmodel displayed using the red-to-green stretch renderer

    4. Turn off the SecuritySubmodel layer by unchecking the check box next to it in the table of contents. Explore the suitability surface values within the FoodSubmodel layer by clicking the map in different locations using the Identify tool Identify, found on the Tools toolbar.

      FoodSubmodel displayed using the red-to-green stretch renderer

    5. Add the FoodSubmodel and SecuritySubmodel layers into the SuitabilityModel model.

      Adding the FoodSubmodel and SecuritySubmodel layers to the ModelBuilder model

    6. The Weighted Sum tool will be used again to combine the three submodels into the final suitability surface. Click the ArcToolbox icon ArcToolbox. Browse to the Weighted Sum tool in the Overlay toolset in the Spatial Analyst Tools toolbox.

      Browsing to the Weighted Sum tool

    7. Drag the Weighted Sum tool into the SuitabilityModel model and place it to the right of the three submodels.

      Adding the Weighted Sum tool to the ModelBuilder model to combine the three submodels

    8. Using the Connect tool Connect in ModelBuilder, connect the three submodels (SecuritySubmodel, HabitatSubmodel, and FoodSubmodel) to the second Weighted Sum tool. Choose the Input raster option each time.

      Connecting the SecuritySubmodel, HabitatSubmodel, and FoodSubmodel layers to the Weighted Sum tool as the Input rasters

    9. Open the second Weighted Sum tool and enter the appropriate weights in the Weight column. Type FinalSuitability in the Output raster parameter. To summarize the input and output layers for the Weighted Sum tool, specify the parameters as follows:
      • Input rasters: SecuritySubmodel, HabitatSubmodel, FoodSubmodel
      • Output raster: FinalSuitability
      • Weight: SecuritySubmodel (2), HabitatSubmodel (1.5), FoodSubmodel (1)

      Weighted Sum tool dialog box with parameters entered

    10. Click OK to apply the changes and close the Weighted Sum tool's dialog box.
    11. Right-click the Weighted Sum tool and click Run to execute the tool.

      Running the Weighted Sum tool that adds the submodels within the model

    12. Right-click the output FinalSuitability layer (green) and click Add To Display to add the output FinalSuitability layer to the map document.

      Adding the results from the Weighted Sum tool that adds the submodels

    13. Choose a red-to-green color ramp for the FinalSuitability layer to help portray each location's suitability. Double-click the FinalSuitability layer in the table of contents and change the Color Scheme under the Symbology tab. To ensure the statistics on the raster are calculated, first select the Classified option from the left panel and if asked, build the histogram by clicking Yes. Then select the Stretched option from the left panel before choosing a red-to-green color ramp from the drop-down options. Click OK once the color ramp has been selected to apply it to the layer.
    14. Save the SuitabilityModeling model by clicking the Save button Save in the ModelBuilder taskbar. Close the model once it is saved.
    15. Explore suitability surface values within the FinalSuitability layer by clicking the map in different locations using the Identify tool Identify, found on the Tools toolbar.

      FinalSuitability layer displayed using the red-to-green stretch renderer

    16. Save the map document by clicking the Save button Save on the Standard toolbar.

    At this point, you have weighted the submodels relative to one another and combined them into a final suitability surface. In Lesson 4: Locating and connecting regions, you will locate and connect the most suitable regions of habitat.