Creating Spatial Feature Classes Based on Proximity, Overlay, and Attributes - Introducing Geographic Information Systems with ArcGIS - page 426

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 by the Output feature class.

25. Perform Overlay with Identity again, but this time use ThreeBars as the Input feature class and
TwoStalks as the Identity feature class. Call the Output feature class IDNTY_B_S_mpp. How
many polygons are in the Output feature class? __________ Note that only polygons in the
areas of the ThreeBars polygons are present in IDNTY_B_S_mpp.

26. Create a feature class named IDNTY_B_S_spp, made by exploding IDNTY_B_S_mpp. How many
polygons are in this feature class? _________.

Exercise 7-4 (Project)

Use Overlay and Extract with Trivial Point and Line
Feature Classes
As discussed in the Overview section of this chapter, Intersect and Identity operations may be used with
point feature classes and line feature classes. Basically, overlays can take place between datasets of the
same dimensionality, or between datasets in which one dataset has a lesser dimensionality than another.
To enumerate:

Polygons and polygons

❏

Polygons and lines

❏

Polygons and points

❏

Lines and lines

❏

Lines and points

❏

Points and points

❏

When you use Overlay with a point feature class, the point feature class is always the Input feature
class and the Output feature class is always a point feature class. The Overlay feature class is
frequently a polygon feature class. With Identity, all of the points in the Input feature class are present
in the output; with Intersect only those points that are in the areas covered by the overlay feature class
are present.

The main thing that happens when you use Overlay with a point feature class and a polygon feature class
is that each point picks up the attributes of the polygon into which it falls. For example, if you had points
representing parking meters and a polygon feature class representing enforcement areas, an overlay of the
two could tell you into which enforcement area each particular parking meter fell. The steps below illustrate
this situation.