Meridian (geography)

In geography, a meridian is an imaginary line that runs from the North Pole to the South Pole, passing through the Earth's surface. Meridians are used to define longitude, which is a measure of how far east or west a point is from the Prime Meridian, which is designated at 0 degrees longitude. Each meridian is measured in degrees, with values ranging from 0° at the Prime Meridian to 180° east or west.