Latitude exact relationship of parallels and meridians with horizontal and vertical: both are complicated curves. On the sphere the normal passes through the centre and the latitude () is therefore equal to the angle subtended at the centre by the meridian arc from the equator to the point concerned. If the meridian distance is denoted by then where denotes the mean radius of the Earth. is equal to . No higher accuracy is appropriate for since higher-precision results necessitate an ellipsoid model. With this value for the meridian length of 1 degree of latitude on the sphere is (60.0 nautical miles).
Latitude to radians, the arc distance is about The distance in metres (correct to 0.01 metre) between latitudes formula_7 − 0.5 degrees and formula_7 + 0.5 degrees on the WGS84 spheroid is The variation of this distance with latitude (on WGS84) is shown in the table along with the length of a degree of longitude (east-west distance): A calculator for any latitude is provided by the U.S. Government's National Geospatial-Intelligence Agency (NGA). The following graph illustrates the variation of both a degree of latitude and a degree of longitude with latitude. Historically a nautical mile was defined as the length of