(12° of longitude in width), and 37X (9° of longitude in width) are extended to cover what would otherwise have been covered by the seven grid zones 31X to 37X. The three grid zones 32X, 34X and 36X are not used. Locating a position using UTM coordinates A position on the Earth is given by the UTM zone number and band letter and the easting and northing planar coordinate pair in that zone and band. The point of origin of each UTM zone is the intersection of the equator and the zone's central meridian. To avoid dealing with negative numbers, the central meridian of each zone is defined to coincide with meters East. In any zone a point that has an easting of meters is about 100 km west of the central meridian. For most such points, the true distance would be slightly more than 100 km as measured on the surface of the Earth because of the distortion of the projection. UTM eastings range from about meters to meters at the equator. In the northern hemisphere positions are measured northward from zero at the equator. The maximum "northing" value is about meters at latitude 84 degrees North, the north end of the UTM zones. The southern hemisphere's northing at the equator is set at meters. Northings decrease southward from these meters to about meters at 80 degrees South, the south end of the UTM zones. Therefore, no point has a negative northing value. For example, the CN Tower is at , which is in UTM zone 17, and the grid position is east, north. Two points in Zone 17 have these coordinates, one in the northern hemisphere and one in the south; the non-ambiguous format is to specify the full zone and band, that is, "17T 630084 4833438". The provision of the latitude band along with northing supplies useful redundant information. Simplified formulae These formulae are truncated version of Transverse Mercator: flattening series, which were originally derived by Johann Heinrich Louis Krüger in 1912. They are accurate to around a millimeter within of the central meridian. Concise commentaries for their derivation have also been given. The WGS 84 spatial reference system describes Earth as an oblate spheroid along north-south axis with an equatorial radius of km and an inverse flattening of . Let's take a point of latitude and of longitude and compute its UTM coordinates as well as