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

Other Polygon Spatial Joins: Intersect and Identity

____ 22. To a new map add TwoStalks and ThreeBars.

____ 23. Again overlay TwoStalks with ThreeBars, but use the Intersect tool rather than Union. Name the Output feature class INTSCT_S_B_mpp, and put it into

___IGIS-Arc_YourInitials\Trivial_GIS_Datasets\ Overlay_Exercise.mdb\Trivial_Feature_Classes

Leave Output Type as INPUT, which will give you polygons.Make sure that INTSCT_S_B_mpp is added to the map. Verify that Intersect computed the geometric intersection of the feature classes, producing new polygons only in the areas common to both feature classes. Use Identify to look at each polygon. Examine the attribute table. Notice that the attributes are the same as for Stalks_Bars_mpp, but of course there are fewer records. How many? _______. Create INTSCT_S_B_spp from INTSCT_S_B_mpp. Now how many records? _______.

____ 24. Perform Overlay with TwoStalks and ThreeBars, but use Identity rather than Intersect. (Read the Help panel.) Use TwoStalks as the Input feature class and ThreeBars as the Identity feature class. Call the Output feature class IDNTY_S_B_mpp. Display on a new map. How many polygons are in the Output feature class? __________. The answer is not 14 (use the Identify tool). Note that only polygons in the areas of the TwoStalks polygons are present in IDNTY_S_B.

When using polygon-on-polygon overlay with the Identity option, it is the areas covered by the Input feature class that determine the area covered ...