Universal Transverse Mercator Coordinate System - Locating A Position Using UTM Coordinates

Locating A Position Using UTM Coordinates

A position on the Earth is given by the UTM zone number and the easting and northing coordinate pair in that zone. The point of origin of each UTM zone is the intersection of the equator and the zone's central meridian, but to avoid dealing with negative numbers the central meridian of each zone is set at 500,000 meters East. In any zone a point that has an easting of 400,000 meters is 100 km west of the central meridian, measured on the transverse Mercator projection (or slightly more than 100 km measured on the actual surface of the earth). UTM eastings range from about 167,000 meters to 833,000 meters at the equator (the range narrows towards the poles). In the northern hemisphere positions are measured northward from zero at the equator; the maximum "northing" value is about 9,300,000 meters at latitude 84 degrees North, the north end of the UTM zones. In the southern hemisphere northings decrease southward from the equator to about 1,100,000 metres at 80 degrees South, the south end of the UTM zones; the northing at the equator is set at 10,000,000 meters so no point has a negative northing value.

The CN Tower is at 43°38′33.24″N 79°23′13.7″W / 43.6425667°N 79.387139°W / 43.6425667; -79.387139 (CN Tower), which is in UTM zone 17, and the grid position is 630084m east, 4833438m north. Two points in Zone 17 have these coordinates, one in the northern hemisphere and one in the south; one of two conventions is used to say which:

1. Append a hemisphere designator to the zone number, "N" or "S", thus "17N 630084 4833438". This supplies the minimum information to define the position uniquely.
2. Supply the grid zone, i.e., the latitude band designator appended to the zone number, thus "17T 630084 4833438". The provision of the latitude band along with northing supplies redundant information (which may, as a consequence, be contradictory).

Because latitude band "S" is in the northern hemisphere, a designation such as "38S" is unclear. The "S" might refer to the latitude band (32°N – 40°N) or it might mean "South". It is therefore important to specify which convention is being used, e.g., by spelling out the hemisphere, "North" or "South", or using different symbols, such as − for south and + for north.