Latitude

Latitude is the angular distance of a location north or south of the Equator, expressed in degrees. It is one half of the most widely used geographic coordinate pair, the other half being longitude. In a geographic coordinate system, latitude identifies position relative to the Equator, which is assigned a value of 0 degrees. Locations north of the Equator are described as north latitude, while locations south of the Equator are described as south latitude. The poles define the limits of latitude. The North Pole is 90 degrees north, and the South Pole is 90 degrees south.

Lines of equal latitude are called parallels because they circle the Earth in planes that are parallel to the Equator. These lines are used in mapping, navigation, geodesy, climate classification, and astronomy. Although latitude is often treated as a simple north or south measurement, its exact value depends on the reference surface used to model the Earth. Because the Earth is not a perfect sphere but an oblate spheroid, modern surveying and satellite systems calculate latitude with reference to a mathematical ellipsoid.

Latitude has long been central to navigation. Ancient astronomers and navigators estimated latitude by measuring the altitude of the Sun at noon or the height of certain stars above the horizon. In the Northern Hemisphere, the altitude of Polaris has historically offered a useful approximation of latitude. Before accurate marine chronometers made longitude easier to determine, latitude was the more accessible coordinate for ocean travel and was therefore a major part of early chartmaking.

Latitude also has broad physical significance. It is closely related to solar angle, day length, and seasonal variation. Areas near the Equator receive sunlight more directly throughout the year, while higher latitudes experience greater seasonal contrast. For that reason, latitude is frequently used in climatology, ecology, and agriculture to describe broad environmental patterns.

In cartography, latitude appears on nearly all global and regional maps. It is commonly written in degrees, minutes, and seconds, or in decimal degrees. A value such as 34.0522 degrees north identifies a place that lies a little more than 34 degrees above the Equator. By itself, latitude narrows a location to an east west band around the Earth. Combined with longitude, it can identify a point with high precision.