ST_ExteriorRing Prev 8.5. Geometry Accessors Next ST_ExteriorRing — Returns a line string representing the exterior ring of the POLYGON geometry. Return NULL if the geometry is not a polygon. Will not work with MULTIPOLYGON geometry ST_ExteriorRing ( geometry a_polygon ) ; Returns a line string representing the exterior ring of the POLYGON geometry. Return NULL if the geometry is not a polygon. Only works with POLYGON geometry types This method implements the OpenGIS Simple Features Implementation Specification for SQL 1.1. 2.1.5.1 This method implements the SQL/MM specification. SQL-MM 3: 8.2.3, 8.3.3 This function supports 3d and will not drop the z-index. --If you have a table of polygons SELECT gid, ST_ExteriorRing(the_geom) AS ering FROM sometable; --If you have a table of MULTIPOLYGONs --and want to return a MULTILINESTRING composed of the exterior rings of each polyg...