ST_Boundary Prev 8.5. Geometry Accessors Next ST_Boundary — Returns the closure of the combinatorial boundary of this Geometry. geometry ST_Boundary ( geometry geomA ) ; Returns the closure of the combinatorial boundary of this Geometry. The combinatorial boundary is defined as described in section 3.12.3.2 of the OGC SPEC. Because the result of this function is a closure, and hence topologically closed, the resulting boundary can be represented using representational geometry primitives as discussed in the OGC SPEC, section 3.12.2. Performed by the GEOS module Prior to 2.0.0, this function throws an exception if used with GEOMETRYCOLLECTION . From 2.0.0 up it will return NULL instead (unsupported input). This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. OGC SPEC s2.1.1.1 This method implements the SQL/MM specification. ...