Oracle Spatial, Geometries

A geometry in Oracle Spatial can be one of the following1: • Point • Linestring connecting two or more points • Polygon specified as a closed linestring and indicating an area bounded by the linestring (with zero or more holes inside the outer bounding linestring) • Multipoint collection • Multiline collection consisting of unconnected linestrings • Multipolygon collection consisting of nonoverlapping polygons, or • Heterogeneous collection consisting of a mixture of point, linestring, and/or polygon geometries Each geometry can be specified in the context of a spatial reference system, also referred to as a coordinate system. Typical coordinate systems are local or geographic. Geographic coordinate systems are geodetic or projected. Whereas local and projected coordinate systems operate in an Euclidean space, geodetic coordinate systems operate on the Earth’s surface. Geometry data in Oracle Spatial can be stored using (1) the SDO_GEOMETRY data type or using (2) the SDO_TOPO_GEOMETRY data type. Whereas the SDO_ GEOMETRY type stores the geometry as is, the SDO_ TOPO_GEOMETRY stores it using simple topological primitive elements such as nodes, edges and faces. The latter representation allows for shared representation of edges (and other elements) between different feature geometries. For instance, a line (or edge) can be shared between the boundary of a land parcel as well as a road segment. The advantages of such shared representation are (1) the ease of topology management across multiple features: changes in the nodes, edges and faces automatically reflect in the higher-level geometry features; (2) elimination of redun-