How Erase works

This topic applies to ArcInfo only.

Erase creates a new output coverage by overlaying two sets of features. The polygons of the erase coverage define the erasing region. Input coverage features that are within the erasing region are removed. The output coverage contains only those input coverage features that are outside the erasing region.

Input Coverage features can be polygons, lines, or points, but erase coverage features must be polygons. Output coverage features are of the same class as the input coverage features. They are clipped to the outer boundary of the erase coverage polygons. Topology is rebuilt for the output coverage.

Erase discovers the feature classes in the input coverage and offers the available erasing methods:

• Poly—Splits the input polygon arcs where they overlap the erase polygons, drops the arcs inside the erase polygons, and builds the remaining arcs into a new polygon coverage. Label points lying outside the erase area are retained, and new polygon label points are generated as required.

  Input region subclasses are maintained and erased. They are maintained as empty subclasses when all the regions have been removed.Route systems are ignored.

• Line—Splits the input arcs where they overlap the erase polygons, drops those portions inside the erase polygons, and builds the remaining arcs into a new line coverage.

  Route systems are duplicated for arcs split into multiple pieces and eliminated for removed arcs.

• Point—Points inside the erase polygons are dropped, and the remaining points are built into a new point coverage.
• Poly & Line (Net)—Polygons and arcs are erased. Polygon topology is rebuilt with an updated PAT and AAT. Route systems are maintained.
• Line & Point (Link)—Arcs and points are erased. Line topology is rebuilt with an updated AAT and PAT.
• Geometry—Arcs, data points, and annotation in a coverage with or without topology (no attribute files) are erased. Route systems are maintained, but regions, PAT, and AAT are not saved.

The attribute table for the output coverage contains the same items as the input coverage feature attribute table. The old feature internal number is used to transfer item information from the input coverage to the output coverage feature attribute tables.

Clip is similar to Erase, except that input coverage features that overlap the clipping region are preserved instead of erased.