longitude

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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.

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.

A diagram of Earth showing lines of longitude, or meridians, running from the North Pole to the South Pole and spaced widest at the equator. The prime meridian is highlighted in red, passing through Europe and Africa. To the right, a list summarizes key facts about lines of longitude, including their direction, measurement, spacing, and relationship to the equator and Earth's axis.

A globe highlighting the location of Washington, D.C. at the intersection of 39 degrees north latitude and 77 degrees west longitude, with labeled latitude and longitude lines, continents, and oceans for global context.

Latitude, longitude, and the prime meridian explained

Investigate the global importance of the Royal Greenwich Observatory and how its location was chosen

longitude

geography

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July 23, 2026

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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. — latitude and longitude Perspective of the globe with grid formed by parallels of latitude and meridians of longitude.

Longitude is a geographical coordinate system used to determine locations on Earth's surface. It measures how far east or west a point is from an imaginary line called the prime meridian. This line runs from the North Pole to the South Pole and passes through Greenwich, London, England.12

Lines of longitude, also known as meridians, run between the geographic poles. They are used in conjunction with lines of latitude (which measure north-south position from the Equator) to create a grid system for precise location identification on maps or globes. Longitude is measured in degrees, with 180 degrees east and 180 degrees west of the prime meridian. The system of standard time zones is based on these meridians, with each zone typically spanning 15 degrees of longitude.324

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latitude and longitude
longitude, in cartography, a coordinate system used to determine and describe the position of any place on Earth’s surface. Latitude is a measurement of a location north or south of the Equator. In contrast, longitude is a measurement of location east or west of the…
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longitude, in cartography, a coordinate system used to determine and describe the position of any place on Earth’s surface. Latitude is a measurement of a location north or south of the Equator. In contrast, longitude is a measurement of location east or west of the…
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map
18th century to the present
…timepiece) made the computation of longitude much less laborious than before; much more information on islands and coastal features came to the map and chart makers.
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…timepiece) made the computation of longitude much less laborious than before; much more information on islands and coastal features came to the map and chart makers.
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Greenwich meridian
…was used to indicate 0° longitude. It passes through Greenwich, a borough of London, and terminates at the North and South poles. Because it indicated 0° longitude, it was also known as the prime meridian. It served as the internationally recognized prime meridian from 1884 to 1984, when it was…
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…was used to indicate 0° longitude. It passes through Greenwich, a borough of London, and terminates at the North and South poles. Because it indicated 0° longitude, it was also known as the prime meridian. It served as the internationally recognized prime meridian from 1884 to 1984, when it was…
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Benjamin Apthorp Gould
…was in charge of the longitude department of the U.S. Coast Survey. In 1859 he published a treatise on the positions and proper motions of the circumpolar stars that were used as standards by the U.S. Coast Survey. Gould was one of the first to use the telegraph to determine…
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…was in charge of the longitude department of the U.S. Coast Survey. In 1859 he published a treatise on the positions and proper motions of the circumpolar stars that were used as standards by the U.S. Coast Survey. Gould was one of the first to use the telegraph to determine…
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Jean Picard
…degree of a meridian (longitude line) and from that computed the size of the Earth.
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…degree of a meridian (longitude line) and from that computed the size of the Earth.
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navigation
Almanacs and tables
…forth the principle of determining longitude by the method of lunar distances—that is, the angular displacement of the Moon from other celestial objects. This method, which was destined to become the standard for a time during the 19th century, remained impracticable for more than three centuries because of the inaccuracy…
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…forth the principle of determining longitude by the method of lunar distances—that is, the angular displacement of the Moon from other celestial objects. This method, which was destined to become the standard for a time during the 19th century, remained impracticable for more than three centuries because of the inaccuracy…
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