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
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.
