Table of Contents
- Tracking Creatures of Bavarian Folklore Using a Least-Cost Path Model
- Setting up Your Workspace
- Preparing the Data
- Skill Drill: Geocoding an Address and Creating a CSV Table to Import As XY Data
- Skill Drill: Defining the Study Area
- Skill Drill: Acquire Elevation Data from the USGS National Map Viewer
- Skill Drill: Acquire Land Cover Data from the USGS National Map Viewer
- Skill Drill: Acquire Hydrography Data from the USGS National Map Viewer
- Changing Global Environment Settings for
- Creating Cost Surface Models Using a Relative Cost Scale
- Creating a Remap Table to Reclassify Elevation
- Skill Drill: Creating a Remap Table to Reclassify Slope
- Skill Drill: Creating a Remap Table to Reclassify Tree Canopy Density
- Converting the Hydrography Features to Cost Surface Models
- Creating a Total Cost Surface Model
- Creating a Cost-Distance Surface Model
- Creating a Migration Corridor
- Determining the Least-Cost Path
- 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.
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.
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.
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.
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.
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.
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.
Remove all previous DEMs from the Table of Contents. You may also remove the ten-mile buffer from the Table of Contents as well.