-1   A value of -1 indicates that the geometry is empty (it does not contain any points).

0   A value of 0 indicates the geometry has no length or area. The subtypes ST_Point and ST_MultiPoint have dimensional values of 0. A point represents a geometric feature that can be represented by a single pair of coordinates, and a cluster of unconnected points represents a multipoint feature.

1   A value of 1 indicates the geometry has length but no area. The set of subtypes that have a dimension of 1 are subtypes of ST_Curve (ST_LineString, ST_CircularString, and ST_CompoundCurve), or collection types containing these types, but no surfaces. In GIS data, these geometries of dimension 1 are used to define linear features such as streams, branching river systems, and road segments.

2   A value of 2 indicates the geometry has area. The set of subtypes that have a dimension of 2 are subtypes of ST_Surface (ST_Polygon and ST_CurvePolygon), or collection types containing these types. Polygons and multipolygons represent geometric features with perimeters that enclose a defined area such as lakes or parks.