Overview of spatial data

The properties of spatial data include the type of spatial object, or geometry, the geographic area where the object is located, and whether the location of the object is measured in angular or linear units.

A geometry is a model of a geographic feature. The coordinates of a geographic feature that a geometry represents are regarded as properties of the geometry. Several kinds of geometries have other properties as well; for example, area, length, and boundary. The types of geometries include points, lines, and polygons. Each geometry is represented by a spatial data type. When you create a table for spatial data, you choose the spatial data type that corresponds to the structure of your spatial data.

When you insert spatial data into the database, you specify a spatial reference system. A spatial reference system is a set of parameters that represents the following characteristics of the location of a geometry:

• The numeric identifier that uniquely identifies the spatial reference system.
• Coordinates that define the maximum extent of space that is referenced by a specified range of coordinates.
• Values for a false origin and system units to store coordinate values at an acceptable scale.
• A text representation of the spatial reference system that describes what type of units the coordinates have.

Whether the coordinates for a geometry are angular or linear units depends on the type of coordinate system to which the geometry conforms. A coordinate system is a framework for defining the relative locations of geometries in a specific area; for example, an area on the Earth's surface or the Earth's surface as a whole. Informix® supports the following types of coordinate systems: geographic coordinate system and projected coordinate systems.

You can convert data between coordinate systems and calculate the distance and area for data that is in either type of system.