The ST_PointOnSurface() function

The ST_PointOnSurface() function takes an ST_Polygon or ST_MultiPolygon and returns an ST_Point guaranteed to lie on its surface.

Syntax

ST_PointOnSurface (pl1 ST_Polygon)
ST_PointOnSurface (mpl1 ST_MultiPolygon)

Return type

ST_Point

Example

The city engineer wants to create a label point for each building footprint.

The buildingfootprints table that was created with the following CREATE TABLE statement stores the building footprints:
CREATE TABLE buildingfootprints (building_id  integer,
                                 lot_id       integer,
                                 footprint    ST_MultiPolygon);
The ST_PointOnSurface() function generates a point that is guaranteed to be on the surface of the building footprints: 
SELECT building_id, ST_PointOnSurface(footprint)
  FROM buildingfootprints;


building_id   506
(expression)  1000 POINT (12.5 49.5) 

building_id   543
(expression)  1000 POINT (32 52.5) 

building_id   1208
(expression)  1000 POINT (12.5 27.5) 

building_id   178
(expression)  1000 POINT (32 30)