Creating Spatial Feature Classes Based on Proximity, Overlay, and Attributes - Introducing Geographic Information Systems with ArcGIS - page 417

12. Look at the attribute table of Buffer_of_Roads_spp. You should see three records. Select each
record and note the corresponding polygon.
13. Use the Multiple Ring Buffer to make another buffer around the roads—this time with a
distance of 111 meters. Call it Buffer_111. Except for the buffering distance, use the same
parameters as before.
14. Arrange the T/C so that Buffer_of_Roads is at the top, with Buffer_111 immediately below it.
Turn off any other entries in the T/C. The feature class Buffer_111 contains only one polygon
instead of three. Why? ________________________________________. ( Hint: Flip the 111-meter
buffer off and on.)
15. Remove the Soils layer. Display the 44-meter buffer with a light yellow. Display the 111-meter
buffer with a dark yellow. Using the Identify feature tool (with the Layer set to Top-most layer),
click the various portions of the buffers, paying attention to what flashes.
16. Use a single application of Multiple Ring Buffer to make a 50 meter buffer and a 100 meter
buffer around Roads, naming the buffer whatever name you want: ___________________. As you
provide input to the tool (it's a Python Script, actually - a term to be defined later) click on the
Dissolve Option and read about the two different options. What are they? __________________.
Use whichever you want and explore the results.
17. Dismiss ArcMap. Dismiss ArcCatalog if it is running.
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.