An entity of type Location can be a Point, Line, Path, Polygon, or Volume. A point has a x and y (and optional z) coordinate. If no z coordinate is specified, sea level is assumed. A line comprises exactly two points. A path is two or more continuous lines. A polygon is the area enclosed by three or more points. A volume is the area enclosed by four or more polygons where each edge is shared by exactly two polygons. Length can be derived from a given Line, area from a given Polygon, and volume from a given Volume.