(UNDER CONSTRUCTION!!)

Universal Transverse Mercator (or UTM) coordinates are typically the standard coordinate system used in spatial air pollution monitoring. UTM coordinates are one way to represent the three-dimensional curved surface of the globe into a flat two-dimensional viewing surface. Like all projection systems the UTM coordinate system results in some distortion when representing the curves surface of the earth.

The UTM coordinate system is broken up into 60 zones. Each representing a strip of surface between the North Pole and South Pole which is 6 degrees of latitude in wide. Each zone has a central meridian (center longitude) where the representation is not distorted. However as the distance between represented surface and the zone's central meridian increases, the distortion increases. The UTM representation can be thought of as projecting the surface of the earth onto a horizontal cylinder which is only touching the earth along the central meridian of one of the zones. The central meridian therefore gives a one to one projection of its surface features, whereas the further away from this line the surface is, the more the distortion increases because of the curvature of the earth.

A GIS spacial data file (or coverage) can be in any of several different types of projections. Each different projection is simply a different way of representing a 3-simensional globe on a 2-dimensional surface. The different types of projections that are supported by Arc/Info are show in table P-1.

Table P-1:

There are two ways to project a coverage into another coordinate system. The projection can either done manually or with the use of a projection file. The manual projection is done with a computer prompting, the projection file method is a one-line command where the projection parameters are pre-written in a text file. The projection file approach is recommended because this allows the operator to go back and review the file if the results are not satisfactory.

The parameters defined in the projection file depend on the projection used. The possible parameter requirements for an Arc/Info supported coverage may include: