Latitude is a coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. It is measured in degrees and ranges from -90° at the south pole to 90° at the north pole. Latitude measures the distance north or south of the equator, which is an imaginary line that circles the Earth at 0° latitude. Latitudes are horizontal lines that measure distance north or south of the equator.
There are different kinds of latitude, including geocentric, astronomical, and geographic (or geodetic), but there are only minor differences between them. Geocentric latitude is the arc subtended by an angle at Earth’s center and measured in a north-south plane poleward from the Equator. Geographic latitude, which is the kind used in mapping, is calculated using a slightly different process. Because Earth is not a perfect sphere, the planet’s curvature is flatter at the poles, so geographic latitude is the arc subtended by the equatorial plane and the normal line that can be drawn at a given point on Earth’s surface.
Latitude and longitude have been used in astronomy and navigation since ancient times. By calculating the angle between the horizon and a celestial object, navigators could determine their approximate latitude using basic tools. The calculations were simple, so measuring latitude at sea was reliable hundreds of years before accurate longitude measurements could be calculated during a voyage.
