Mobile Location Services: The Definitive Guide

Geographical Data Types

To understand how map databases store information, it is important to understand the basic geographic data types used to represent real-world geographic phenomena. In the vector data model, geographic data is stored in discrete points, lines, and polygons. Points, lines, and polygons are respectively zero-, one-, and two-dimensional static representations of real-world phenomena in terms of simple x, y coordinates.

Points

Points refer to objects that have location and attribute information, but are not large enough to be represented as areas (see Figure 4.6). Whether an object is represented as a point or a polygon depends on the level of abstraction and scale of the map. Cities that would be represented as points in a ...