SPATIAL DATABASES

In the entity-based model of space, space is composed of spatial objects that are entities with explicit identity and whose spatial components (i.e., spatial data types) can be of the following types:

 

zero-dimensional entities or points

one-dimensional entities, linear objects or curves, whose basic geometry type is a polyline that is defined by a finite set of line segments or edges such that segment endpoints, except extreme points of the polyline, are shared by exactly two segments. Different variants of polylines are closed polylines whose extreme points are identical; simple polylines, where no pair of nonconsecutive edges intersect at any place; and monotone polylines with respect to a line µ, where every line µ’ orthogonal to µ meets the polyline at one point at most.

 

Figure: (a) closed polyline, (b) non-simple polyline, and (c) non-monotone polyline.

 

Two-dimensional entities or surface objects, whose main geographic type is a polygon that is defined by a region bounded by a closed polyline. Variants of polygons are simple polygon if its boundary is a simple polyline, convex polygon if the segment between any pair of points in the polygon is fully included in the polygon, and monotone polygon is its boundary is a monotone polyline.

Figure: (a) simple polygon, (b) non-simple polygon, (c) convex polygon, and (d) monotone polygon.

The identification of basic spatial data types and their interrelations has reached a consensus in the proposal of the Open GIS consortium standard.

Figure: Basic spatial data types and their interrelations in UML (based on specification OpenGIS).