Geographic Information Systems: An Introduction, 3rd Edition

6.2 Coordinate Systems

In mathematics there are, in principle, two different methods for designating a point's location. The location of a point may be designated:

• As an angle and distance
• As coordinates in a right-angled cartesian coordinate system

A position can therefore be indicated by distance and direction from the origin. This is known as the polar coordinate system (Figure 6.3). Polar coordinates can be transformed relatively easily to cartesian coordinates without loss of precision, provided one is operating within the same datum. In practice, the angle of the new point is measured in relation to one or more known points (see Figure 6.4).

In geodesy, the most usual right-angled coordinate systems are:

• Geocentric coordinates, where x, y, and z are given in a triple-axle system with the origin in the Earth's center
• Geographic coordinates, where latitude and longitude are stated on the Earth's sphere
• Map projection coordinates, where North and East, or x and y, are given on one plane

Figure 6.3

Example of unique positioning finding rectangular coordinates and polar coordinates.

Figure 6.4

The polar location of a point is measured as the direction and distance from other fixed points in the terrain.

A coordinate system is defined in full by name, the measuring units, and ...