Area(mpoly)

Returns as a double-precision number the area of the MultiPolygon value mpoly, as measured in its spatial reference system.

mysql> SET @mpoly =
    -> 'MultiPolygon(((0 0,0 3,3 3,3 0,0 0),(1 1,1 2,2 2,2 1,1 1)))';
mysql> SELECT Area(GeomFromText(@mpoly));
+----------------------------+
| Area(GeomFromText(@mpoly)) |
+----------------------------+
|                          8 |
+----------------------------+

Centroid(mpoly)

Returns the mathematical centroid for the MultiPolygon value mpoly as a Point. The result is not guaranteed to be on the MultiPolygon.

PointOnSurface(mpoly)

Returns a Point value that is guaranteed to be on the MultiPolygon value mpoly.