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

Skill Drill: Acquire Elevation Data from the USGS National Map Viewer

To complete the least-cost path analysis, you will need an elevation layer. In previous courses, you learned how to acquire data from public sources. Here you will download digital elevation models from the USGS National Map Viewer. You will then combine the two digital elevation models into one layer and clip the new raster layer to the 10-mile buffer. Navigate to the USGS National Map Viewer at https://viewer.nationalmap.gov/basic/. Click on the link to download GIS data. This link will take you to the map viewer.

An image of the USGS National Map Viewer landing page.
The USGS National Map is an excellent source of many different types of data for the United States.

On the right, zoom in and center the map to the approximate region of interest. On the left, under Elevation Products, check the box next to 1/3 arc-second DEM. Then click. Find Products.

An image of the National Map Viewer Data Selection page
To acquire data for a specific region, you must use the map to zoom to that location.

On the Products tab, you will see a list of datasets available for download. To determine which digital elevation models cover the area of interest, you can click on the Footprint link to see the boundary of the dataset. At this time, two digital elevation models cover the region of interest. Click the Download link to download each one. Save the files in your original folder and decompress them.

An image of the National Map Viewer Products page
Unlike recent changes to the USGS Earth Explorer, downloading data from the National Map Viewer is very easy to do. Just click on the download link.

In ArcMap, add the two digital elevation models to the map. If you look carefully, you will see the seam between the two digital elevation models. To continue, you will need to combine these two DEMs into one raster dataset. As you will recall from previous coursework, you can do this by using the tool Mosaic to New Raster, located in the Raster Dataset toolbox.

An image of the DEMs Added to ArcMap
Most tools in ArcGIS will require a single raster dataset as input. If you have a region that overlaps with two or more raster datasets, you will have to combine them into one layer.

The Mosaic to New Raster tool has settings that require particular attention. The Output Location is looking for a folder, not a file name. Students often get confused with this setting. Enter the name of the file in the next field, Raster Dataset Name with Extension. I typically use the .img extension or the .tif extension to avoid limitations on the length of the file name. Be sure there are no spaces in the file name. Use underscores in place of empty spaces instead. The Mosaic to New Raster tool will also allow you to project the raster datasets as well. Under Spatial Reference for Raster, choose NAD 83 UTM Zone 10 N. The Pixel Type settings is also very important. By default, the output of this tool is an 8 BIT pixel depth. If the original datasets have a more substantial pixel depth, you will lose quite a bit of information. Always make sure the Pixel Type setting matches the original data. In this instance, you want to change the Pixel Type to 32 Bit Floating Point. A digital elevation model has only one band. Enter the number 1 under Number of Bands. You may leave all other settings as default. Once you are ready, click OK. The result will be a single, seamless digital elevation model.

An image of the Moasaic to new raster tool

The final step in preparing the digital elevation model is to clip it to the 10-mile buffer around the den locations and the town of Orick. In ArcMap, vector and raster data often use different versions of the same type of tools. When performing a clip operation on a raster dataset, the Clip tool found under the Geoprocessing menu will not work. Instead, you should use the Clip tool located in the Raster Processing toolbox.

An image of the Clip tool under Raster Processing toolbox

This clip tool defines the output extent as a rectangle based on the layer used in the Output Extent field. In this instance, it uses the 10-mile buffer you created in a previous step. Save the output to your working folder. This result will be the final digital elevation model you will use for your least-cost path analysis. Leave the other settings as default and click OK.

An image of the clip tool

Remove all previous DEMs from the Table of Contents. You may also remove the ten-mile buffer from the Table of Contents as well.

An image of the Results of the Dem Clip Operation
To clip a raster dataset, you will have to use a different version of the clip tool. Confusingly, this tool has the same name as the tool under the Geoprocessing menu. In the image above, the raster dataset has been clipped to the extreme North, South, East, and West boundaries of the buffer.