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

Floating-Point Rasters

If the following math stuff leaves you scratching your head, don’t worry about it. The point is that Spatial Analyst can do a lot of esoteric operations on rasters. Just go with the flow, even if the details escape you.

____ 19. Bring up a new map without saving changes to the former one. Find and start the Create Random Raster (Spatial Analyst) tool in ArcToolbox. For the Output raster, browse to the folder Raster_Experiments > Ras_Expr.gdb and call the new raster Ran_Ras. Save. Leave the Seed value for the pseudorandom number generator blank.4 For the output cell size, use 100. For the Output extent, use the four numbers you wrote down above (x & y minima, x & y maxima) for Basic_Raster. OK the window. The raster Ran_Ras will be added to the map.

____ 20. Ran_Ras consists of 42 cells, whose values are approximately uniformly distributed between zero and one. For Symbology, pick a Color Ramp that goes from light to not too dark. Use the Identify tool to examine four values (to three significant digits). _______, _______, _______, _______. Use the CellTool to light up the whole raster with values.

____ 21. Ran_Ras contains numbers in the range zero to one. Suppose that instead you wanted to have integer numbers between 1 and 10 put in the cells. You could use the Int function (make into an integer) in the Raster Calculator on Ran_Ras. You will find Int in the box to the right of the Boolean buttons. Place this expression in the Raster Calculator:

Int((“Ran_Ras” ...