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 Remap Table to Reclassify Elevation

To assign a relative scale to a cost factor, you will use the reclassify tool. Your first step will be to reclassify the elevation layer.  After careful study, the researchers evaluated which elevations the wolpertinger likes best. They believe the wolpertinger is most likely to want to travel through areas of higher elevation. When using the Reclassify tool in the past, you may have entered the break values manually everytime the tool was run. For most purposes, manually entering break values works fine. However, there may be situations when you want to run a model multiple times and would like the ability to easily and accurately change parameters. In this instance, a remap table is useful. A remap table is a specially formatted table used by the Reclassify tool to define how the data will be reclassified. The remap table must contain the fields FROM, TO, OUT, and MAPPING. The FROM field defines the lower limit of a data range. In this example, the lowest value in the digital elevation model is -0.99247. For the first data range, a -1 has been entered in FROM field to ensure that each of the lowest pixel values is captured by the remap table. The TO field defines the upper limit of a data range. In this example, the last data range is from 1000 to 1613. The highest value in the digital elevation model is 1612.91. By entering 1613 in the TO field, you ensure that each of the highest pixel values is captured by the remap table. The OUT field defines the new values replacing the old values by the Reclassify tool. In this example, the first range is FROM -1 TO 1. Since 10 is entered under the OUT field, any pixel within this range will have an output value of 10. Unfortunately, there is not much documentation about The MAPPING field or its specific purpose. However, it is required by the Reclassify tool. You must enter ‘ValueToValue’ under this field for each data range. In Microsoft Excel, create the remap table shown below. Save the table in your working folder as a comma-separated value (CSV) file. When you are done, be sure to close Microsoft Excel.

FROMTOOUTMAPPING
-1110ValueToValue
11007ValueToValue
1002006ValueToValue
2004005ValueToValue
4006004ValueToValue
6008003ValueToValue
80010002ValueToValue
100016131ValueToValue

In ArcMap, open the Reclassify tool. This tool can be found in the Reclass toolbox under the Spatial Analyst Tools.

An image of the Reclass Toolbox

Enter the clipped digital elevation model as your Input Raster. The Reclass field should automatically populate. Click the Load button to load the remap table you created. You may have to navigate to your working folder to find it. Once loaded, you should see the Old values and New values in the Reclassify tool match up with the values in your remap table. Save the Output Raster to your working folder. As an extra precaution, check the box next to Change missing values to NoData. This step will ensure that any values not covered by the remap table will be removed. Once you are ready, click OK.

An image of the reclassify tool

The digital elevation model has now been reclassified using the remap table. Hopefully, you will have found using a remap table much easier than manually entering in the reclassification values. This layer now represents the relative cost or likelihood, on a scale of 1 through 10, that this species will traverse each pixel based on elevation.

An image of the elevation cost loaded into ArcMap
In this image, the ArcGIS software has assigned random colors to the pixel values between 1 and 10. Your results should look similar. Be sure there are no values beyond 1 through 10.