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Latitude bands "A" and "B" do exist, as do bands "Y" and Z". They cover the western and eastern sides of the Antarctic and Arctic regions respectively. A convenient mnemonic to remember is that the letter "N" is the first letter in the northern hemisphere, so any letter coming before "N" in the alphabet is in the southern hemisphere, and any letter "N" or after is in the northern hemisphere. The combination of a zone and a latitude band defines a grid zone.
The zone is always written first, followed by the latitude band. For example see image, top right , a position in Toronto, Canada, would find itself in zone 17 and latitude band "T", thus the full grid zone reference is "17T". The grid zones serve to delineate irregular UTM zone boundaries. They also are an integral part of the military grid reference system.
A note of caution: A method also is used that simply adds N or S following the zone number to indicate North or South hemisphere the easting and northing coordinates along with the zone number supplying everything necessary to geolocate a position except which hemisphere. However, this method has caused some confusion since, for instance, "50S" can mean southern hemisphere but also grid zone "50S" in the northern hemisphere. These grid zones are uniform over the globe, except in two areas.
The three grid zones 32X, 34X and 36X are not used. The easting is the projected distance of the position from the central meridian, while the northing is the projected distance of the point from the equator.
The point of origin of each UTM zone is the intersection of the equator and the zone's central meridian. In order to avoid dealing with negative numbers a false origin is used.
False origins are located south and west of the true origin, and thus create values known as false easting and northing. The central meridian of each zone is given a false easting value of , meters. Thus, anything west of the central meridian will have an easting less than , meters. For example, UTM eastings range from , meters to , meters at the equator these ranges narrow towards the poles. In the northern hemisphere, positions are measured northward from the equator, which has an initial "northing" value of 0 meters and a maximum "northing" value of approximately 9,, meters at the 84th parallel — the maximum northern extent of the UTM zones.
In the southern hemisphere, northings decrease as you go southward from the equator, which is given a false northing of 10,, meters so that no point within the zone has a negative northing value.
This is in zone 17, and the grid position is m east, m north. There are two points on the earth with these coordinates, one in the northern hemisphere and one in the southern. The polar regions use the Universal Polar Stereographic coordinate system.
The origin for each zone is its central meridian and the equator. To eliminate negative coordinates, the coordinate system alters the coordinate values at the origin. The value given to the central meridian is the false easting, and the value assigned to the equator is the false northing. A false easting of , meters is applied. A north zone has a false northing of zero, while a south zone has a false northing of 10,, meters. Cylindrical projection. See the "Transverse Mercator" topic for the methodology.
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