The output map data set contains the newly defined unit areas. These new unit areas are created by removing all interior line segments from the original unit areas. All variables in the input map data set except X, Y, SEGMENT, and the variables listed in the BY statement are omitted from the output map data set.

The output map data set might contain missing X, Y coordinates to construct any polygons that have enclosed boundaries (like lakes or combined regions that have one or more hollow interior regions).

The SEGMENT variable in the output map data set is ordered according to the size of the bounding box around the polygon that it describes. A SEGMENT value of 1 describes the polygon whose bounding box is the largest in the unit area, and each additional SEGMENT value describes a smaller polygon. This information is useful for removing small polygons that clutter up maps.

All current unit areas with common BY-variable values are combined into a single unit area in the output map data set. The new unit area contains the following: