Overlay analysis is one of the basic GIS spatial operations. It is a process
of generating new data through set operations on vector datasets. The
application program provides overlay analysis functions for point, line, and
region datasets. Common overlay analysis functions include Clip, Union, Erase,
Intersect, Identity, Symmetrical difference, and Update.
Introduction to Overlay Analysis
It contains detailed descriptions of basic concepts about overlay analyses and the logical operations involved in overlay analyses.
Overlay Analysis Operators
The basic concepts and principles of the 7 overlay analysis operators are described in details here.
Clip
Clip is a process of extracting feature parts (points, lines, or regions) from a source dataset (clipped dataset) using an overlay dataset (clip dataset).
Union
Union is a function for performing the union operation on a source dataset and an overlay dataset.
Erase
Erase is a process of erasing the parts of the source dataset (the erased dataset) using the overlay dataset (the erase dataset). The erased parts are the overlapped parts of the two datasets.
Intersect
Intersect is a process of finding the intersection of a source dataset (intersected dataset) and an overlay dataset (intersect dataset).
Identity
Identity is a process of performing an Intersect operation on a source dataset and an overlay dataset.
XOR
XOR is a process of performing a negation operation on the intersection of a source dataset and an overlay dataset.
Update
Update is a process of replacing object parts in a source dataset (updated dataset) with corresponding parts in an overlay dataset (update dataset) where the two datasets overlap.