The zone number refers to the zone, divided longitudinally every 6 degrees. Zone 1 begins at 180degrees West Longitude (International Date Line). Zone 13 begins at 108degrees West Longitude (around Grand Junction, CO).

The letter refers to the grid, divided latitudinally every 8 degrees. Grids go between C and X. (Why they didn't start with A must have something to do with the polar regions and issues related to that.) Grid C starts at 80degrees South Latitude. Grid S starts at 32degrees North Latitude (about at the Texas panhandle).

Most of Colorado falls into UTM grid cell 13 S, with some in 13 T, 12 S and 12 T. Utah is divided in half between 12 S and 12 T.

Therefore a complete UTM coordinate contains a zone number and letter and the X and Y coordinates (along with a datum you are working in).  (e.g. 12 S  0501120E, 4357850N NAD 27.)

Websites that illustrate or discuss UTM coordinates can be found at:

http://www.dmap.co.uk/utmworld.htm


http://mapping.usgs.gov/mac/isb/pubs/factsheets/fs15799.html#projections


>>>Org. question:
When working in UTM coordinates, what do the S and T refer to which come up on my GPS unit? Is that letter important to know if I am providing waypoint coordinates to someone else for GIS mapping or GPS navigation purposes? Could anyone recommend a book chapter, or web site which discusses the UTM coordinate system, hemispheres, zones, and the S & T issue?


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Chris Colt
Habitat Biologist/GIS Specialist
Utah Division of Wildlife Resources
475 W. Price River Dr. #C
Price, UT 84501
ph. (435)636-0279
nrdwr.ccolt@state.ut.us
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