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

Variable-Width Buffers

As you know, a single layer may contain many features. The features usually have different attributes that distinguish features from each other. For example, in Roads there are some graphic features that are associated with RD_CODE “1” and others with RD_CODE “2.” Suppose that you wanted to buffer the “1” roads with a distance “x” and the “2” roads with a distance “y.” You can do the following:

____ 18. Start ArcMap. Add Roads from the Wildcat_Boat geodatabase in ___IGIS-Arc_YourInitials. Represent the features by a red line of width 2.

____ 19. Open the attribute table. Under Options add a field named Buffer_by. Make it a Short Integer field.

____ 20. Start editing with the Editor toolbar. Note that a tiny pencil shows up at the bottom of the table. Suppose that you want to buffer the RD_CODE = 1 roads by 20 meters and the RD_CODE = 2 roads by 40 meters. Notice that the first records have a 1 in RD-CODE, so we would want to put 20 in the Buffer_by attribute of those records. Click the Buffer_by field cell in the first record and type 20. Now do the same with the second record. And the third. This looks like a long haul. We’ll use another way instead.

____ 21. On the Main menu, choose Selection. Select By Attributes. Construct the expression [RD-CODE] = 1. See Figure 7-14. Click Verify. If the expression is OK, click Apply, then OK to close the Select By Attributes window. Now you can see that all the records with 1 in the RD_CODE are selected.

FIGURE ...