Geography Reference
In-Depth Information
Ras_Expr.gdb, calling it Bas_Ras2. Click OK and, shortly, Bas_Ras2 will be added to the map
when the Raster Calculator is finished. Verify that it is identical to Basic_Raster (despite the
fact that different colors are used for the cell values).
Arithmetic Calculation
One of the simplest such operations involving rasters is adding them. When two rasters that represent
the same geographic space and have the same cell sizes are added together, each cell of the resulting
raster contains the sums of the cells in equivalent locations. In the next step, you will explore the Raster
Calculator a bit more and then add the two rasters you have made.
14. Start the Raster Calculator again. Click Tool Help and look at the Illustration. You can come
back to this if you have questions regarding the operation of the Raster Calculator. Close the
help window.
15. You will sum the two rasters to produce a third raster. The expression to do this is
“Basic_Raster” + “Bas_Ras_2”
You can do this in much the way you made expressions earlier: double-click the particular
raster you want and single-click the operators or digits. Place this expression in the middle box.
Browse and put the output in Ras_Expr.gdb, calling it Bas_Ras_Sum. See Figure 8-38. Click OK.
The new raster will be added to the map. Use Identify, the T/C, the CellTool, and the Bas_Ras_
Sum attribute table to convince yourself that each cell contains the correct value. 2
FIGURE 8-38
2 You may have noticed that the raster names aren't particularly consistent when it comes to capitalization of
letters. ArcMap may refer to Bas_Ras_Sum, while ArcCatalog may refer to the same raster as bas_ras_sum, Think
of the ArcGIS software as an old house that got added onto. You are currently in an older part of the house where
capitalization is sort of ignored. Just be content that you don't have to look at everything in all capital letters. (Also,
newer versions of the software may hang onto your capitalization; if so, appreciate it.)
 
 
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