LESSON 2: SCALES AND PROJECTIONS
III. Spatial Measurement Scales
C. Plane Coordinate Systems: UTM
The Universal Transverse Mercator system is not really universal, but it does cover nearly the entire Earth surface. Only polar areas-latitudes higher than 84º North and 80º South--are excluded. The system divides the remainder of the Earth's surface into 60 zones, each covering 6º of longitude. 

"Transverse Mercator" refers to the manner in which geographic coordinates are transformed into plane coordinates. Such transformations are called map projections. We will consider map projections in detail later in this lesson. For now, an illustration will suffice. The animation below shows a series of 60 Transverse Mercator projections that form the 60 zones of the UTM system. The zones are numbered 1 to 60 eastward from the international date line. 
Figure 2.08: Sequence of 60 Transverse Mercator projection. A unique projection is used for every UTM zone, so that deformation within each zone is minimized.

Play the above animation to view each UTM zone in red.
Each UTM zone is subdivided along the equator into two halves, north and south. Every half of every UTM zone is a separate plane coordinate system. The north-south axes of both halves are 10 million meters in length, the distance between the equator and the poles. The north-south axes are located 500,000 meters west of the zone's central meridian. Therefore, the x,y coordinate pair denoting every position in a UTM coordinate system zone is a positive number, where x is greater than 0 and less than 1,000,000 meters, and y is greater than 0 and less than 10,000,000 meters. 
Figure 2.09: Characterstics of one UTM Zone. Source: Muerhcke, P.M. and Muerhcke, J.O. (1988) Map Use (3rd ed.)

The advantage of UTM coordinates over the geographic coordinate system of latitudes and longitudes is that positive distance values are easier to work with than positive and negative angular values. There are also disadvantages, however. Coordinates of large features that cross over UTM zone boundaries need to be transformed into common measurement scales. Furthermore, since all plane coordinate systems involve map projections, and all map projections involve deformation, positions specified by UTM coordinates are displaced from their actual locations by as much as 1 part in 2,500. Deformation increases with distance from two standard lines (shown in red).

Select the self-test icon at the top of the page to answer practice questions about UTM Coordinates.

Remember, self-tests are not graded and can be taken as many times as you like.