
Data Standards  Coordinate Systems
A coordinate
system is used to define a location on the Earth. It is created
in association with a map projection,
datum, and
reference ellipsoid and describes locations
in terms of distances or angles from a fixed reference point. The
system may be either a Cartesian system, with coordinates based
on orthogonal or 90degree angles, or it may be polar, based on
angles measured from a point such as the center of the Earth. For
example, in the latitude/longitude system, positions are described
based on angular measurements north or south of the equator and
east or west of the Prime Meridian, which runs through Greenwich,
England. This is considered a polar system [See Figure 1].
Coordinates are used to describe positions in
two or threedimensional space and specify a particular location.
A twodimensional system uses a coordinate pair, typically referred
to as X and Y, to describe a horizontal position on the Earth. A
threedimensional system adds the height or elevation to create
an X, Y, Z position.
Figure 1: Example of a Polar System (SIC
2002).
Some coordinate systems extend over the entire
globe, while others are used exclusively for specific regions of
the Earth. Examples of global coordinate systems include Latitude/Longitude,
Universal Transverse Mercator (UTM), World Geographic Reference
System (WGRS), and various military grid reference systems. Examples
of local coordinate systems include numerous national grid systems,
as well as Universal Polar Stereographic, which is used for the
polar regions of the globe.
