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

Considering the Site Eccentricity Criterion

We have one more selection to perform. Recall that the site eccentricity may not be more than 4.6 unless the total area of the polygon is greater than 7000 square meters.

____ 10. Add another field to the table of Sites_D. Name it Eccentricity. Since the number will contain decimal places and we are not sure of its range, specify the Type as Float. Click OK.

____ 11. Right-click the Eccentricity column head; pick Field Calculator. Ignore the warning. Write the expression you need to use in the following blank: ___________________________________. Put the expression in the Field Calculator window, then check it against Figure 7-25. When you have it right, Click OK.

FIGURE 7-25 Wildcat eccentricity calculation

The Attributes of Sites_D window will have eccentricities ranging from just over 4 to about 6 and a half.

____ 12. Clear any selected records or polygons. Use Analysis Tools > Extract > Select to apply the criterion. Write the SQL Expression that will let you use Sites_D to make a feature class called Final_NEW_Sites, that satisfies this additional requirement. ____________________________________________. Wait to look at Figure 7-26 until you have written your expression. Select the proper polygons with the Select tool. How many are there? ____

FIGURE 7-26 Size and Eccentricity selection

____ 13. Display Final_NEW_Sites, ...