ST_MultiPolygon data type

The ST_MultiPolygon data type defines features such as a forest stratum or a non-contiguous parcel of land such as an island chain.

Properties

The boundary of an ST_MultiPolygon is the cumulative length of its elements' exterior and interior rings. The interior of an ST_MultiPolygon is defined as the cumulative interiors of its element ST_Polygons. The boundary of an ST_MultiPolygon's elements can only intersect at a tangent point. In addition to the other properties inherited from the superclass ST_Geometry, ST_MultiPolygons have area.

The following figure shows examples of ST_MultiPolygon: (1) is ST_MultiPolygon with two ST_Polygon elements. The boundary is defined by the two exterior rings and the three interior rings; (2) is an ST_MultiPolygon with two ST_Polygon elements. The boundary is defined by the two exterior rings and the two interior rings. The two ST_Polygon elements intersect at a tangent point.
Figure 1: Examples of ST_MultiPolygon objects

This graphic is described in the surrounding text.

Functions

The following functions that operate on ST_MultiPolygons:
ST_Area()
The function returns the cumulative area of its ST_Polygon elements as a double-precision number.
ST_Centroid()
The function returns an ST_Point that is the center of an ST_MultiPolygon's envelope.
ST_PointOnSurface()
The function returns an ST_Point that is guaranteed to be on the surface of one of its ST_Polygon elements.