Longitude is an angular coordinate around a chosen polar axis, measured from a reference half-plane. On Earth the conventional reference is the Greenwich meridian. In a Cartesian coordinate convention it is , with a specified range such as .
Together with latitude and a radius it describes a point using spherical coordinates. Longitude is undefined at the poles because every meridian meets there. Its numerical jump at the chosen meridian cut is a coordinate discontinuity, not a discontinuity of the sphere itself. On an oblate reference ellipsoid, geographic latitude needs an additional geodetic convention.
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Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is measured in degrees (°), with the Prime Meridian (0° longitude) serving as the starting reference line. The Prime Meridian runs from the North Pole to the South Pole, passing through Greenwich, London, England.