Point on surface

A representative point guaranteed to lie on (or inside) a polygon, often used for labeling.

Category: Geometry · Also known as: interior point, label point, ST_PointOnSurface

Definition (expanded)

A centroid can land outside concave polygons or polygons with holes. A point-on-surface (sometimes called an interior point) is computed to guarantee it lies on the polygon surface/area, making it better for labels and markers.

Examples

PostGIS point on surface

SQL

SELECT ST_AsText(ST_PointOnSurface(geom)) FROM my_polygons;

Common mistakes

Using centroid for labeling and being surprised when the label appears outside the polygon.

Related terms

CentroidA representative center point of a polygon, often used for labeling or quick location.PolygonA closed area geometry defined by an exterior ring and optional interior rings (holes).Hole (Interior Ring)An interior ring inside a polygon that subtracts area (a cut-out).PointA single coordinate location, represented as one (x, y) pair.