A circle of latitude, on the Earth, is an imaginary east-west circle connecting all locations (not taking into account elevation) that share a given latitude. A location's position along a circle of latitude is given by its longitude.
Circles of latitude are often called parallels because they are parallel to each other. On some map projections, including the Equirectangular projection, they are drawn at equidistant intervals.
Circles of latitude become smaller the farther they are from the equator and the closer they are to the poles. A circle of latitude is perpendicular to all meridians at the points of intersection, and is hence a special case of a loxodrome.
Contrary to what might be assumed from their straight-line representation on some map projections, a circle of latitude is not, with the sole exception of the Equator, the shortest distance between two points lying on the Earth. In other words, circles of latitude (except for the Equator) are not great circles (see also great-circle distance). It is for this reason that an airplane traveling between a European and North American city that share the same latitude will fly farther north, over Greenland for example.
Arcs of circles of latitude are sometimes used as boundaries between countries or regions where distinctive natural borders are lacking (such as in deserts), or when an artificial border is drawn as a "line on a map", as happened in Korea.
Major circles of latitude
There are five major circles of latitude, listed below from north to south, with their values (Epoch 2010).:
These circles of latitude, excluding the Equator, mark the divisions between the five principal geographical zones.
The equator is the circle that is equidistant from both the North Pole and South Pole. It divides the Earth into the Northern Hemisphere and the Southern Hemisphere.
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