Creating Spatial Feature Classes Based on Proximity, Overlay, and Attributes - Introducing Geographic Information Systems with ArcGIS - page 434

22. Explode the multipart polygons that Union makes, using the Multipart To Singlepart tool.
Call the resulting feature class Union_So_Ow_Wt. Look at its attribute table. Now how many
polygons are there? _______________
23. Add Getrich_County to the map. Since the gold lies within the county boundaries, you can limit
yourself to the part of Union_So_Ow_Wt that lies within Getrich County. Fortunately there is a
tool that will trim away the area we don't need to look at. Use ArcToolbox > Analysis Tools >
Extract > Clip. Determine by reading the sidebar Help what needs to go in each field. Give the
resulting feature class the name GR_Cnty_only. Use the T/C to display that feature class by
itself on the map. Use Identify to check out a number of polygons, paying attention to whether
the gold might be there, based on CHARACTERISTIC, Wagt_areas, and OilwNoGold.
24. As the final analysis step, you will use ArcToolbox > Analysis Tools > Extract > Select. Start
the Select tool. For input, use GR_Cnty_only. Name the output Look_Here. Before you run the
tool, write in the space that follows the expression you will enter in the SQL section in order to
extract the polygons that represent the areas that must be searched. (By the way, you may want
to use the operator <>, which means “not-equal”. Strictly speaking, A <> B means either A is
less than B or A is greater than B—which is the same as saying A cannot be equal to B.)
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25. Enter the expression, making good use of the Get Unique Values button. (To check the
expression you just wrote - hey, now, try to do this on your own first - look at Figure 7-18.) Click
Verify. Click OK. Click OK.
26. Make the polygons of Look_Here bright yellow. Make the polygons of GR_Cnty_only a light pink.
The map should look like Figure 7-19. Verify, from both the Identify tool and the attribute table,
that they satisfy the original problem requirements. How many areas are there? ________.
27. From the attribute table create Statistics on the areas of Look_Here. In the worst case, where
you have to look at all possible areas, how many areas would have to be searched? ________.
How much area would have to be searched? ________ How much would it cost to search it, at
$0.02 per square meter? _____________ Would you invest in the search? ________.
Suppose it cost $0.03 per square meter. Would you invest in the search? ________. Why or why
not? (Think about probabilities.)
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FIGURE 7-18 Select string for gold