# Meridian (geography)

In geography and geodesy, a **meridian** is the locus connecting points of equal longitude, which is the angle (in degrees or other units) east or west of a given prime meridian (currently, the IERS Reference Meridian).[1] In other words, it is a **line of longitude**. The position of a point along the meridian is given by that longitude and its latitude, measured in angular degrees north or south of the Equator. On a Mercator projection or on a Gall-Peters projection, each meridian is perpendicular to all circles of latitude. A meridian is half of a great circle on Earth's surface. The length of a meridian on a modern ellipsoid model of Earth (WGS 84) has been estimated as 20,003.93 km (12,429.87 mi).[2]

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