Geodesy the ellipsoid varies with latitude, being the longest at the pole and the shortest at the equator as is the nautical mile. A metre was originally defined as the 10-millionth part of the length from equator to North Pole along the meridian through Paris (the target was not quite reached in actual implementation, so that is off by 200 ppm in the current definitions). This means that one kilometre is roughly equal to (1/40,000) * 360 * 60 meridional minutes of arc, which equals 0.54 nautical mile, though this is not exact because the two units are defined on different
Cylindrical equal-area projection many named specializations such as Gall–Peters or Gall orthographic, Behrmann, and Lambert cylindrical equal-area). This divides north-south distances by a factor equal to the secant of the latitude, preserving area but heavily distorting shapes. Any particular cylindrical equal-area map has a pair of identical latitudes of opposite sign (or else the equator) at which the east–west scale matches the north–south scale. All cylindrical equal-area projections use the formula: where "λ" is the longitude, "λ" is the central meridian, "φ" is the latitude, and "φ" is the standard latitude, all expressed in radians. Some cartographers prefer to work in degrees, rather