Tracking Creatures of Bavarian Folklore Using a Least-Cost Path Model

Table of Contents

  1. Tracking Creatures of Bavarian Folklore Using a Least-Cost Path Model
  2. Setting up Your Workspace
  3. Preparing the Data
  4. Skill Drill: Geocoding an Address and Creating a CSV Table to Import As XY Data
  5. Skill Drill: Defining the Study Area
  6. Skill Drill: Acquire Elevation Data from the USGS National Map Viewer
  7. Skill Drill: Acquire Land Cover Data from the USGS National Map Viewer
  8. Skill Drill: Acquire Hydrography Data from the USGS National Map Viewer
  9. Changing Global Environment Settings for Raster Processing
  10. Creating Cost Surface Models Using a Relative Cost Scale
  11. Creating a Remap Table to Reclassify Elevation
  12. Skill Drill: Creating a Remap Table to Reclassify Slope
  13. Skill Drill: Creating a Remap Table to Reclassify Tree Canopy Density
  14. Converting the Hydrography Features to Cost Surface Models
  15. Creating a Total Cost Surface Model
  16. Creating a Cost-Distance Surface Model
  17. Creating a Migration Corridor
  18. Determining the Least-Cost Path
  19. Skill Drill: Creating a Map of the Results

Creating a Cost-Distance Surface Model

In this scenario, you want to model movement between the wolpertinger dens and the town of Orick as they migrate into town during the Oktoberfest season. To do this, you need to know how cost increase as the species moves both away from the town of Orick and as it moves away from the dens. You will use the Path Distance tool which calculates the accumulative cost over a cost surface. The Path Distance tool calculates the Euclidean distance between cells and origin features. However, it also incorporates changes in elevation when determining distance. As distance increases from origin feature, cells are assigned a cumulative travel cost based on both distance and cost surface values. It stores the cumulative cost moving outward from the origin. In ArcMap, the origin is sometimes called the source feature In this step, you will use the Path Distance tool twice. You will run it first using the town of Orick as the source feature, then again using the den locations layer as the source. In ArcMap, open the Path Distance tool. This tool can be found in the Distance toolbox under the Spatial Analyst Tools.

An image of the Distance toolbox

Under Input raster or feature source data, use the layer representing the town of Orick. For the Output distance raster, navigate to your working folder and name the output Orick_Cost_Distance.img.

Don’t forget to add the .img extension in order to avoid file name restrictions. Alternatively, you may use .tif as well. Also, depending on the speed of your computer, it may take up to 10 minutes for the path distance tool to run. To avoid crashes, try not to click on ArcMap while the tool is running.

For the Input Cost raster, choose your total cost surface model. For the Input surface raster, browse to your clipped digital elevation model. This step will allow the Path Distance tool to account for changes in elevation when calculating distance. For the Output backlink raster, navigate to your working folder and name the output Orick_backlink.img. Leave all other settings as default and click OK.

An image of the Path Distance tool

The result will be two new raster layers added to ArcMap, one cost-distance model, and one backlink raster. The backlink raster contains cells with values ranging from 0 through 8. These cells track the direction along the least-cost path from anywhere on the surface back to the origin. In a later step, you will use both the cost-distance model and the backlink to determine a least-cost path.

An image of the Cost Distance and Backlink rasters side by side
The image on the left shows the cumulative cost from as you move outward from the town of Orick. The image on the right shows the backlink raster generated by the Path Distance tool. These two layers will not appear side by side in ArcMap and are arranged this way for demonstration purposes only.

Using the same methods, open the Path Distance tool again to create a cost-distance surface utilizing the den locations for the Input raster or feature source data.  You will not need to create a backlink raster for the den locations.

An image of the path distance tool

When you are done with this step, you should have two cost-distance models, one for the den locations and one for the town of Orick. Next, you will use both cost-distance models to create a migration corridor.

An image of the Cost Distance model for den locations
In this image, the den cost-distance layer records the cumulative cost as you move away from the individual dens. The pixel values are assigned costs based on the nearest den.