Introducing Geographic Information Systems with ArcGIS: A Workbook Approach to Learning GIS, 3rd Edition

Examining Many Source Cells and the Capping Distance

____ 12. In the T/C turn off Onecell and MapDist1. Add the raster Manycells to the map. Notice the presence of several cells containing data, while the rest of the raster shows No Data. There is still a single source cell in the southwestern portion of the raster, but there is also a line of source cells in the northeast and a clump (cluster) of source cells in the northwest. What are the values of the three zones? ________, ________, ________. Change the colors of all the source cells to black.

You will generate a raster containing distances to the nearest source cells, provided that the distance is no further than 30 kilometers. You can limit the search for the closest source cell so that it does not exceed a given value, thereby excluding cells in the output raster that are more than a certain distance away from any source cell. (Those cells will contain NO DATA.) You are telling the software “if you have to look further than this to get to a source cell, just forget it.” Such a number may be called a limit, a cap, a cutoff value, or a threshold.

____ 13. Use the same Spatial Analyst tool (Euclidean Distance) as you did in the previous steps to create the new distance raster from Manycells. Browse to make its name DistManycells. In the text box for Maximum distance, type 30. The Output cell size should be 10. Click OK.

The raster of source cells that serves as input to this tool may consist of several single cells, ...