Spatial data types

Spatial Data Types

Several spatial data types can be used to represent the spatial extent of real world objects. , we use the spatial data types defined by the conceptual spatiotemporal model MADS ]. These data types and their associated icons are shown in diagram below As shown in the figure, these data types are organized in a hierarchy and provide support for two-dimensional features.

SimpleGeo is a generic spatial data type that generalizes the types Point, Line, and Surface. SimpleGeo is an abstract type, i.e., it is never instantiated as such: upon creation of a SimpleGeo value it is necessary to specify which of its subtypes characterizes the new element. A SimpleGeo value can be used, for instance, to generically represent cities, whereas a small city may be represented by a point and a bigger city by a simple surface.

ComplexGeo represents any heterogeneous set of geometries that may include sets of points, sets of lines, and sets of surfaces. ComplexGeo may be used, for instance, to represent a water system consisting of rivers (oriented lines), lakes (surfaces), and reservoirs (points). ComplexGeo, has PointSet, LineSet, OrientedLineSet, SurfaceSet, and SimpleSurfaceSet as subtypes.

Point represents zero-dimensional geometries denoting a single location in space. A point can be used to represent, for instance, a village in a country.

Line represents one-dimensional geometries denoting a set of connected points defined by one or more linear (in) equations. A line can be used to represent, for instance, a road in a road network. A line is closed if it has no identifiable extremities (in other words, its start point is equal to its end point)

OrientedLine represents lines whose extremities have the semantics of a start point and an end point (the line has a given direction from the start point to the end point). OrientedLine is a specialization of Line. An oriented line can be used to represent, for instance, a river in a hydrographic network.

 

Surface represents two-dimensional geometries denoting a set of connected points that lie inside a boundary formed by one or more disjoint closed lines. If the boundary consists of more than one closed line, one of the closed lines contains all the other ones, and the latter represent holes in the surface defined by the former line. In simpler words, a surface may have holes but no islands (no exterior islands and no islands within a hole).

SimpleSurface represents surfaces without holes. For example, the extent of a lake may be represented by a surface or a simple surface, depending on whether the lake has or not islands.

Several spatial data types are used to describe spatially homogeneous sets.

PointSet represents sets of points, which could be used to represent, for instance, the houses in a town.

LineSet represents sets of lines, which could be used to represent, for instance, a road network.

OrientedLineSet (a specialization of LineSet) represents a set of oriented lines, which could represent for instance, a river and its tributaries.

 SurfaceSet and SimpleSurfaceSet are used for sets of surfaces with or without holes, respectively, and are useful, for instance, to represent administrative regions.