A geometry can have a dimension of 0, 1, or 2. The dimensions are listed as follows:
The point and multipoint subclasses have a dimension of zero. Points represent dimensional features that can be modeled with a single coordinate, while multipoint subclasses represent data that must be modeled with a cluster of disconnected coordinates.
The subclasses linestring and multilinestring have a dimension of one. They store road segments, branching river systems and any other features that are linear in nature.
Polygon and multipolygon subclasses have a dimension of two. Features whose perimeter encloses a definable area, such as forests, parcels of land, and water bodies can be rendered by either the polygon or multipolygon data type.
Dimension is important not only as a property of the subclass, but it also plays a part in determining the spatial relationship of two features. The dimension of the resulting feature or features determines whether or not the operation was successful. DB2 Spatial Extender examines the dimension of the features to determine how they should be compared.
The ST_Dimension function takes a geometry and returns its dimension as an integer. For more information, see ST_Dimension.