Longitude those points (unless on the equator, where these are equal); the difference is less than . A geographical mile is defined to be the length of one minute of arc along the equator (one equatorial minute of longitude), therefore a degree of longitude along the equator is exactly 60 geographical miles or 111.3 kilometers, as there are 60 minutes in a degree. The length of 1 minute of longitude along the equator is 1 geographical mile or , while the length of 1 second of it is 0.016 geographical mile or . Planetary co-ordinate systems are defined relative to their
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