Overlay from Operations of Vector Data: Point-In-Polygon Overlay, Line-In-Polygon Overlay, and Polygon-In-Polygon Overlay (Especially for GATE-Geospatial 2022)

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In addition to simply combining layers, querying them, and comparing them, layers can be combined to produce new layers through geometric intersections. This is called overlay. Any of the three types of vector data can be overlaid with any of the others. This has many potential uses.

Overlay is one of the most important functions of GIS. These involve combining different feature type (point, line, area) from different layers to produce a new map containing features and attributes of user interest.

Types of Overlay Operations

There are of three types:

Diagram Shows Three Types of Overlay

1. Point-In-Polygon Overlay

Overlay point coverages on polygon coverage. It computers contained in relationship and the resulting point coverage contains new attributes. E. g. combine wells and planning districts, find district containing each well.

Figure Shows Point-In-Polygon Overlay

2. Line-In-Polygon Overlay

Overlay line objects or area object, compute β€œis contained in” relationship. Lines are broken at each area object boundary for e. g. number of output lines is greater than number of input lines containing area is new attribute of each output line. E. g. combine streams and counties, find country containing each stream segment.

Figure Shows Line-In-Polygon Overlay

3. Polygon-In-Polygon Overlay

Overlay two layers of area objects boundaries are broken at each intersection number of output areas likely greater than the total number of input areas e. g. input watershed boundaries, county boundaries, output map of watershed/country combinations after overlay we can recreate either of the input layers by dissolving and merging based on the attributes contributed by the input layer.

Figure Shows Polygon-In-Polygon Overlay

Types of Polygon-In-Polygon Overlay Operations

Polygon-in-polygon overlay operations are of three types:

Diagram Shows Types of Polygon-In-Polygon Overlay


The UNION procedure is equivalent to the Boolean operator β€œOR” in which two or more data layers are overlaid to produce a combined coverage. Every polygon in the output coverage carries the attribute information of both the input and union coverage.


The INTERSECT procedure is equivalent to the Boolean AND operation. When the two coverages are overlaid, only portion of the input coverage that falls inside the intersect coverage will remain in the output coverage.


The IDENTITY overlay function everything located within the boundaries of the input coverage is collected in the output coverage. The boundary of the output coverage is identical to the input coverage.

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