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

Improving the Understandability of the Map

You can get a better idea of travel times by redoing the legend of Drive Time. The current legend simply breaks the drive times up into equal intervals, resulting in unwieldy ranges. A better set of classes can be defined, and a better legend can be created.

____ 21. Through Drive_Time Properties, bring up Symbology. In the Show box, select Classified. Specify 10 classes, then press Classify. In the Classification window, pick Manual for the Classification Method and make the break values 3, 5, 10, 15, 20, 25, 30, 40, 50, and 60. Click OK. Back in Layer Properties pick a color ramp you like. In the Label column, type in the top value of each range: 3, 5, and so on. Click Apply, then OK. Look again at the T/C entry for Drive_Time. Better?

The new legend uses more appropriate and readable divisions of driving time.

____ 22. Close all legends except ROADS, Off_ramps, and Drive_Time. Clear any selected features. Make the symbol for Off_ramps and ROADS solid black. From the top to the T/C, order the layers: ROADS, Off_ramps, and Drive_Time. Turn them on and everything else off. Explore the resulting map, using Identify on the Drive_Time raster. Click in a number of cells—both at full extent and zoomed in.

It should be apparent that the mathematical massaging you did earlier (calculating minutes per foot) to make the ultimate results show up as minutes was worthwhile.

____ 23. Use File > Save As to save the project with a new name: ...