An overview of the Overlay toolset

This topic applies to ArcInfo only.

Contains tools to overlay multiple coverages to combine features into or erase, modify, or update spatial features in a new coverage.

New information is created when one set of features is overlaid with another. There are five types of overlay operations. All involve joining two existing sets of features into a single set of features to identify spatial relationships between the input features.

For the Erase, Intersect, and Identity tools, the input coverage can be either a point, line, or polygon coverage. However, for the Update and Union tools, the input coverage must be a polygon coverage.

In all cases, the action coverage (for example, erase coverage) must be a polygon coverage. The output coverage contains the same feature class as the input coverage, and topology is built.

For the Union, Update, Identity, and Intersect tools, the attribute table of the output coverage contains attribute fields from both the input and action coverage. The attribute fields (items) are merged using the original internal numbers of each feature. For the Erase tool, only the attributes of the input coverage exist in the output coverage. These features, too, have the same internal number as the original input coverage.

Tool	Description
Erase	Creates a new output coverage by overlaying the polygons of the erase coverage with the features of the input coverage. Only those portions of the input coverage features falling outside the erase polygon outside boundaries are copied to the output coverage.
Identity	Computes the geometric intersection of two coverages. All features of the input coverage, as well as those features of the identity coverage that overlap the input coverage, are preserved in the output coverage.
Intersect	Computes the geometric intersection of two coverages. Only those features in the area common to both coverages will be preserved in the output coverage.
Union	Computes the geometric intersection of two polygon coverages. All polygons from both coverages will be split at their intersections and preserved in the output coverage.
Update	Replaces the input coverage areas with the update coverage polygons using a cut and paste operation.