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Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition by Michael D. Kennedy

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Creating Direction and Allocation Rasters
You learned that you can calculate the shortest distance between two places using the Euclidean Distance request and you can find the least-cost path with the Cost Distance request, but there may still be a couple of major questions: (1) Which source cell is closest to (or least expensive to reach from) each given cell in the raster, and (2) what is the direction or path from each given cell?
Going back to the Euclidean (straight line on the map) calculation, you will be able to make not only a raster showing the distance to a source cell as you did previously, but you will make two additional rasters. One of these will show, in each cell, approximately, the direction one must travel to get to a source cell. The second will show, in each cell, the number of the closest source cell. You will use the two parameters in the Euclidean distance request that were left unchecked in previous examples.
____ 25. In ArcMap click File > Open. Open Proximity_startup.mxd.9 Add the layer Twocells to the map.
____ 26. Find and start the Euclidean Allocation tool. The Input raster should be Twocells. Source field: Value. The output cell size should be 10. Max Distance should be 50. Browse to the Prox_Exp.gdb and name the Output raster Eucl_Allocation_Twocells. Make the Output distance raster Eucl_Distance_Twocells and the Direction raster Eucl_Direction_Twocells_dir. Click OK.
____ 27. Arrange the layers in the T/C this way:
Square_Grid
Twocells ...

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