Latitude, usually denoted symbolically by the Greek letter phi, , gives the location of a place on Earth north or south of the Equator. Latitude is an angular measurement in degrees (marked with °) ranging from 0° at the Equator to 90° at the poles (90° N for the North Pole or 90° S for the South Pole). All locations of a given latitude are collectively referred to as a circle of latitude or line of latitude or parallel, because they are coplanar, and all such planes are parallel to the Equator. Lines of latitude other than the Equator are approximately small circles on the surface of the Earth; they are not geodesics since the shortest route between two points at the same latitude involves moving farther away from, then towards, the equator.

A specific latitude may then be combined with a specific longitude to give a precise position on the Earth's surface.

Each degree of latitude is further sub-divided into 60 minutes. One minute of latitude is one nautical mile, defined exactly as 1852 meters (this is approximate due to slight variation with latitude (at sea level) and is because the earth is slightly oblate). One minute of latitude can be further divided into 60 seconds. A latitude is thus specified as 13°19′43″ N. For high accuracy, the seconds are specified with a decimal fraction. An alternative representation uses degrees and minutes, where parts of a minute are expressed as a decimal fraction, thus: 13°19.717′ N. Degrees expressed as a decimal number (decimal degree notation) is more often used: 13.32861° N. Sometimes, the north/south suffix is replaced by a negative sign for south (−90° for the South Pole).

Important named circles of latitude

Four lines of latitude are named because of the role they play in the geometrical relationship with the Earth and the Sun:

Only at latitudes between the Tropics is it possible for the sun to be at the zenith. Only north of the Arctic Circle or south of the Antarctic Circle is the midnight sun possible.

The reason that these lines have the values that they do lies in the axial tilt of the Earth with respect to the sun, which is 23° 26′ 22″.

Text based on information from Wikipedia and available under the terms of the GNU Free Documentation License.