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meridian
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A three-dimensional globe featuring a grid of latitude and longitude lines, with labeled parallels, meridians, the Equator, Prime Meridian, and North Pole. A specific point at 40 degrees north, 30 degrees west is marked, and directional arrows indicate north, south, east, and west. Clock with Roman numerals Cutaway illustration of a globe showing how latitude and longitude are measured as angles from the center of the Earth. The diagram highlights New Orleans at 30 degrees north latitude and 90 degrees west longitude, with labeled lines for the equator, prime meridian, axis, and key continents for reference.
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latitude and longitude
latitude and longitude Perspective of the globe with grid formed by parallels of latitude and meridians of longitude.

meridian

geography
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Clock with Roman numerals
Clock with Roman numeralsA 12-hour clock with Roman numerals.

meridian, imaginary north–south line on the Earth’s surface that connects both geographic poles; it is used to indicate longitude. The 40th meridian, for example, has a longitude of 40° E or 40° W. See latitude and longitude. The prime meridian is zero degrees longitude and divides Earth into the Western and Eastern hemispheres. It is also known as the Greenwich Meridian because it passes through Greenwich, a borough of London, and terminates at the North and South poles. The meridian is also a key element in timekeeping, as in the 12-hour clock.