Welcome to lesson 1 of the cost-distance analysis workflow. Cost-distance analysis is a form of spatial analysis that measures how costly, or expensive, it is to travel over a surface. Cost-distance analysis simulates how a mover will experience the landscape as they travel through it. This is different from Euclidean distance, which captures how far a mover is from known locations in a straight line.
Cost can be measured in time, dollars, energy expended, or other forms.
The lessons will walk you through how to most effectively connect the bobcat patches that were identified in the suitability case study (see Lesson1: Exploring and deriving data). This lesson will walk you through how to create a cost surface, which is essential for all cost-distance analysis workflows. Lesson 2 will demonstrate how to create the optimum network of paths to connect the bobcat patches identified in the suitability case study. Lesson 3 will show how to create the optimum least-cost path between a known source and destination, and lesson 4 will identify how to create a wildlife corridor between two patches.
Creating a cost surface follows similar steps to creating a suitability surface. As in creating a suitability surface, when creating a cost surface, criteria that influence the cost of movement are identified, placed on a common scale, weighted, and combined. Unlike in the final suitability surface where the higher values are more preferred, in the cost surface, the lower values are more preferred (representing lower costs).
This lesson is divided into seven sections:
- Downloading and preparing the tutorial data
- Exploring your data and opening and editing the ModelBuilder model
- Deriving criteria from base data (elevation)
- Using the Reclassify tool to transform categorical data (land use)
- Using the Rescale by Function tool to transform continuous criteria (slope)
- Weighting and combining criteria in a submodel
- Weighting and combining submodels into the overall model
ArcGIS Spatial Analyst extension is required for this analysis and you must ensure that it is enabled. See Enabling the Spatial Analyst extension.
These lessons were created in ArcGIS Desktop using version 10.4.1.
Downloading and preparing the tutorial data
- Download the data package at the beginning of this case study.
- Browse to the ZIP file in the Downloads folder.
- Unzip the ZIP file named CostDistanceAnalysis.
- Copy the unzipped CostDistanceAnalysis directory (which contains Data.gdb, Output.gdb, the Toolbooxes folder, and several MXD files) onto the C drive.
Exploring your data and opening and editing the ModelBuilder model
- Open the CostSurface map document by double-clicking the file.
- Two layers are in the table of contents: Landuse and Elevation. First explore the land use map by clicking the map with the Identify tool
(found on the Tools toolbar).
- Turn off Landuse by unchecking the check box next to it in the table of contents. Turn on Elevation by checking the check box next to it. Now explore the Elevation surface as you did with the land use using the Identify tool .
- To help keep the different cost-distance analysis workflows organized, the tools will be tracked in several ModelBuilder models. Within the CostDistanceAnalysis folder is a folder named Toolboxes, with a toolbox named CostDistanceAnalysisToolbox.tbx, which contains several models. One of these models will be used to create a cost surface for this lesson. Open ArcCatalog by clicking the ArcCatalog icon
in the taskbar, which will open the Catalog window. From the Catalog window, open the CostSurface model by right-clicking the model and clicking Edit.
Deriving criteria from base data (elevation)
Because bobcats respond either directly or indirectly to land use and elevation when traveling, these criteria will be incorporated within an energy submodel in the cost surface model.
- Drag the Landuse and Elevation layers from the table of contents into the CostSurface model and align them vertically.
- The Slope tool requires Spatial Analyst, so 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.
- Click the ArcToolbox button
in the taskbar at the top of the map document.
- Browse to the Slope tool by clicking the Spatial Analyst Tools toolbox and then the Surface toolset.
- Drag the Slope tool into the model and place it to the right of the Elevation layer.
- Using the Connect tool
in the CostSurface ModelBuilder model taskbar, connect the Elevation layer to the Slope tool. Make the connection by clicking the Elevation layer first, and then click the Slope tool. Choose the Input raster option.
- Double-click the Slope tool within the CostSurface model to open the tool's dialog box. Type Slope in the Output raster parameter to name the output slope raster. The model automatically saves the file into the Output.gdb geodatabase file. To summarize the input and output layers for the Slope tool, specify the parameters as follows:
- Input raster data: Elevation
- Output raster: Slope
- Click OK to close the Slope tool's dialog box.
- Once the dialog box is closed, right-click the Slope tool and click Run to execute the tool.
- Add the output Slope layer to the map document by right-clicking the green Slope(2) layer and clicking Add To Display.
- Explore the Slope layer within the CostSurface map document. According to the legend, locations that have a gentle or flat slope are green, intermediate slopes are yellow, and steep slopes are red.
Using the Reclassify tool to transform categorical data (land use)
Next, the Reclassify tool will be used to transform the values of the Landuse layer onto a common scale. Once both the slope and land use criteria have been transformed onto the same scale, they can be combined into a single layer for the energy submodel within the cost surface model. For more information on transforming data, see the Transforming data onto a common preference scale story map. The Reclassify tool is used to transform the land use values because the data is categorical.
- Click the ArcToolbox button on the Standard toolbar. Browse to the Reclassify tool in the Spatial Analyst Tools toolbox in the Reclass toolset.
- Drag the Reclassify tool into the CostSurface model and place it to the right of the Landuse dataset.
- Connect the Landuse dataset in the model to the Reclassify tool by using the Connect tool . Once the icon is selected, first click the Landuse layer and then click the Reclassify tool. Click Input raster.
- Double-click the Reclassify tool (yellow rectangle) to open it and enter the following parameters, including the transformed values for each land use category listed in the table. You could reclassify using the CLASS_NAMES field, but since you are only interested in the resulting reclassed values, to simplify the resulting output table and the default symbology the VALUE field will be used.
- Input raster: Landuse
- Reclass field: VALUE
- Output raster: Reclass_Landuse
VALUE New values Descriptions (for reference only) 1
10
Developed, High Intensity
2
10
Developed, Medium Intensity
3
9
Developed, Low Intensity
4
7
Agriculture
5
5
Grassland
6
2
Forest, Deciduous
7
1
Forest, Coniferous
8
2
Forest, Mixed Deciduous-Coniferous
9
4
Scrub/Shrub
10
4
Wetland
11
8
Bare Land
12
10
Water
- Click OK to close the Reclassify tool's dialog box in which you entered the above parameters.
- Right-click the Reclassify tool and click Run to execute the tool.
- Add the output Reclass_Landuse layer to the display by right-clicking the green output circle and clicking Add To Display.
- Choose a red-to-green color ramp for the Reclass_Landuse layer to help portray each location's cost based on land use. Double-click the Reclass_Landuse layer in the table of contents and change the Color Scheme on the Symbology tab. Select the Stretched display of values from the left pane before choosing a red-to-green color ramp from the drop-down options. Check the Invert check box toward the bottom of the main pane to align red colors with values of high cost and green colors with values of low cost. Click OK once the color ramp has been selected to apply it to the layer.
Using the Rescale by Function tool to transform continuous criteria (slope)
In order to combine the land use and slope criteria into a single submodel pertaining to energy expenditure, transform the slope data onto the same common scale used for land use. Slope data is continuous data; therefore, a continuous function is used to transform its values using the Rescale by Function tool.
- Browse to the Rescale by Function tool in the ArcMap toolboxes .
- Drag the Rescale by Function tool into the CostSurface model and place it to the right of the output Slope(2) layer (green).
- Use the Connect tool tool in ModelBuilder taskbar to add the Slope(2) output layer to the Rescale by Function tool as the Input raster.
- Double-click the Rescale by Function tool to open it and enter the following parameters:
- Input raster: Slope (2)
- Output raster: Rescale_Slope
- Transformation function: Large
- From scale: 1
- To scale: 10
- Click OK to save the changes made to the Rescale by Function tool.
- Right-click the Rescale by Function tool and click Run to execute the tool.
- Right-click the output Rescale_Slope layer (green) and click Add To Display to add the output Rescale_Slope layer to the map document.
- Change the color ramp of the Rescale_Slope layer so that green indicates areas of low cost. Double-click the Rescale_Slope layer in the table of contents and click the Symbology tab. Choose a red-to-green color ramp from the drop-down list. Check the Invert check box toward the bottom of the main pane. Click OK to save the changes.
Weighting and combining criteria into a submodel
Now that the slope and land use criteria are on the same common scale, they can be combined using the Weighted Sum tool to create the energy expenditure submodel surface.
- Browse to the Weighted Sum tool in the ArcMap toolboxes .
- Drag the Weighted Sum tool into the CostSurface model and place it to the right of the transformed datasets.
- Using the Connect tool in the ModelBuilder taskbar, connect the two layers of transformed data (Reclass_Landuse and Rescale_Slope) to the Weighted Sum tool icon. Choose the Input rasters for both layers.
- Open the Weighted Sum tool by double-clicking it, and enter the appropriate weights in the Weight column. Save the output raster as EnergySubmodel in the Output raster parameter and save it within the Output.gdb file geodatabase.
- Input rasters: Reclass_Landuse, Rescale_Slope
- Output raster: EnergySubmodel
- Weights: Reclass_Landuse (1), Rescale_Slope (1)
- Click OK to save the changes made to the Weighted Sum tool.
- Right-click the Weighted Sum tool and click Run to execute the tool.
- Add the output EnergySubmodel layer to the display by right-clicking the green output layer and clicking Add To Display.
- Choose a red-to-green color ramp for the EnergySubmodel layer to help portray each location's cost based on energy use. Double-click the EnergySubmodel layer in the table of contents and change the Color Scheme on the Symbology tab. To ensure the statistics on the raster are calculated, first choose the Classified option from the left pane and if asked, build the histogram by clicking Yes. Then choose the Stretched display of values from the left pane before choosing a red-to-green color ramp from the drop-down options. Check the Invert check box toward the bottom of the main pane to align red colors with values of high cost and green colors with values of low cost. Click OK once the color ramp has been chosen to apply it to the layer.
- Explore cost surface values within the EnergySubmodel layer by clicking the map in different locations using the Identify tool (found on the Tools toolbar).
Weighting and combining submodels into the overall model
To create the final cost surface, the EnergySubmodel will be added to two other submodels already created and available in the Data.gdb file geodatabase: ResourcesSubmodel and SecuritySubmodel. The ResourcesSubmodel and SecuritySubmodel submodels measure costs related to sustenance and physical safety, respectively.
- Drag the ResourcesSubmodel and SecuritySubmodel layers from the Data.gdb file geodatabase into the table of contents.
- As you just did for the EnergySubmodel, choose a red-to-green color ramp for the ResourcesSubmodel and SecuritySubmodel layers to help portray each location's cost 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 pane before choosing a red-to-green color ramp from the drop-down options. Check the Invert check box toward the bottom of the main pane to align red colors with values of high cost and green colors with values of low cost. Click OK once the color ramp has been selected to apply it to the layer.
- Explore the values of the ResourcesSubmodel and SecuritySubmodel using the Identify tool (found on the Tools toolbar).
Resources submodel—Costs of travel increase farther away from food sources.
Security submodel—Costs of travel increase closer to roads and buildings.
- From the table of contents, drag the ResourcesSubmodel and SecuritySubmodel into the CostSurface model, where they will be combined with the EnergySubmodel to create the final cost surface. Place them underneath the EnergySubmodel output layer.
- In the ArcMap toolboxes , browse to the Weighted Sum tool in the Overlay toolset in the Spatial Analyst Tools toolbox, and add it to the CostSurface model.
- Using the Connect tool in ModelBuilder, connect the three submodel layers (EnergySubmodel, ResourcesSubmodel, and SecuritySubmodel) to the Weighted Sum tool icon. Choose the Input rasters option for each.
- Open the Weighted Sum tool by double-clicking it, and enter the appropriate weights in the Weight column. Specify the output raster as CostSurface in the Output raster parameter and save it within the Output.gdb file geodatabase.
- Input rasters: EnergySubmodel, ResourcesSubmodel, SecuritySubmodel
- Output raster: CostSurface
- Weights: EnergySubmodel (1), ResourcesSubmodel (1), SecuritySubmodel (1.5)
- Click OK to save the parameters and close the dialog box.
- Run the Weighted Sum tool by right-clicking the Weighted Sum tool icon (yellow) and clicking Run.
- Add the CostSurface output layer (green) to the map document by right-clicking the CostSurface layer and clicking Add To Display.
- Save the CostSurface model by clicking the Save button
in the ModelBuilder taskbar. Close the model once it is saved. - Change the colors in which the cost surface is displayed to better indicate high-cost and low-cost areas. Double-click the CostSurface layer in the table of contents and open the Symbology tab. To ensure the statistics on the raster are calculated, first choose the Classified option from the left pane and if asked, build the histogram by clicking Yes. Choose a Stretched display of values from the pane on the left side. From the drop-down list of color ramps, choose a red-to-green color scheme. Invert the direction of the colors by checking the Invert check box near the lower right of the main pane. Click OK once the color ramp has been selected to apply it to the layer.
- Explore cost surface values by clicking the map in different locations using the Identify tool (found on the Tools toolbar).
- Save the CostDistanceAnalysis map document by clicking the Save button on the Standard toolbar.
Congratulations! You have successfully created a cost surface, which is used in all the following lessons for the different cost-distance analysis workflows. In Lesson 2: Creating an optimal connectivity network, the cost surface will be used to connect the optimum bobcat patches identified in Lesson 4:_Locating and connecting regions of the suitability modeling workflow.