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Union
Union operations combine polygons with polygons and keep all geometry.
Union acts like the Boolean OR operation and can be used only with polygons.
For example, you can combine parcels with soils information for property
assessment. Use Union to maintain both sets of geometry together and pull
them apart as needed.
Identity
Identity operations work like Union on the source topology and like Intersect
on the overlay topology. Use Identity to combine nodes, links, or polygons
with polygons and keep all the input geometry. Identity creates one topology
with one link where the link is crossed by the overlay topology.
When Identity is used with the question, Which parcels (polygons) fall within
100-year flood zones (polygons)?, all the properties in the flood zones are
shown intact.
Erase
Erase operations use the overlay polygon topology like a mask and erase
everything in the source polygon topology that is covered by the overlay
topology.
Clip
Clip operations use the overlay polygon topology as a boundary. The parts of
the source polygons outside the overlay polygons are clipped and discarded.
You can use this option to show polygons within a boundary polygon, such
as a city or state boundary.
Paste
Paste operations paste the overlay polygon topology on top of the source
polygons. The source polygons not covered by the overlay remain. The Paste
option can be used only with polygons.
Object Data in Overlay Analysis
You can copy selected object data and external database data from the source
and overlay topologies to a new object data table in the resulting topology.
You specify the name of the new object data table that will store the data in
the resulting topology. The object data table name should be a new name.
Data fields in the resulting topology look like this:
TOPONAME_FIELD
1338 | Chapter 8 Analyzing Data