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

Making New Sites that Include the COST_HA Field

____ 6. Start ArcMap. Show ArcToolbox. Bring up the Dissolve (management) tool. Remake Sites_C from Sites_A, using Dissolve, but this time put a check in the COST_HA box, to preserve this field in the Sites_C table. Be sure to make singlepart polygons. Verify that the COST_HA field exists in the attribute table. Use Analysis Tools > Extract > Select to make Sites_D by applying the “greater than or equal to 4000” criterion to the Shape_Area of Sites_C. When computation stops, turn off all layers in the T/C except Sites_D Look at the table of Sites_D, and verify again that you do indeed have the COST_HA field. Also verify that the boundaries you wanted to lose are gone. (There is the one little worry that two adjacent polygons might have different land cover values, and that by running the Dissolve tool we might have left some troublesome boundaries. Here is where visual inspection gets into the process. Examine Sites_D to assure yourself that no connected polygons exist.)

____ 7. Find the Options button on the attributes table of the Sites_D window. Add a field named SITE_COST to the Sites_D table. Its type should be Float, because its values will be calculated with an expression involving the floating-point numbers of Shape_Area. If any of the operands of an expression are floating point, then the results must also be floating point.

____ 8. Right-click the SITE_COST column head. Select Field Calculator. Ignore the warning. In ...