180th meridian

The 180th meridian or antimeridian[1] is the meridian 180° both east and west of the prime meridian in a geographical coordinate system. The longitude at this line can be given as either east or west.

"Anti-Meridian" redirects here. For the Brave Saint Saturn album, see Brave Saint Saturn § Discography.
Not to be confused with ante meridiem (AM), the time before midday, for which see 12-hour clock.
A map of the Earth with the Pacific Ocean in the centre, with a vertical red line running the full height just west of the Bering Strait and east of New Zealand.
The 180th meridian on a map of Earth.
The International Date Line zigzags around the 180th Meridian.

On Earth, the prime and 180th meridians form a great circle that divides the planet into the Western and Eastern Hemispheres. The antimeridian passes mostly through the open waters of the Pacific Ocean but also runs across land in Russia, Fiji, and Antarctica. An important function of this meridian is its use as the basis for the International Date Line, which snakes around national borders to maintain date consistency within the territories of Russia, the United States, Kiribati, Fiji and New Zealand.

Starting at the North Pole of the Earth and heading south to the South Pole, the 180th meridian passes through:

Co-ordinates
(approximate)		 Country, territory or sea Notes
90°0′N 180°0′E Arctic Ocean North Pole
71°32′N 180°0′E  Russia Chukotka Autonomous Okrug — Wrangel Island
70°58′N 180°0′E Chukchi Sea
68°59′N 180°0′E  Russia Chukotka Autonomous Okrug
65°02′N 180°0′E Bering Sea
52°0′N 180°0′E Amchitka Pass Passing just east of Semisopochnoi Island, Alaska,  United States (at 51°57′N 179°47′E)
51°0′N 180°0′E Pacific Ocean Passing just east of Nukulaelae atoll,  Tuvalu (at 9°25′S 179°52′E)
Passing just west of the island of Cikobia-i-Lau,  Fiji (at 15°43′S 179°59′W)
16°9′S 180°0′E  Fiji Islands of Vanua Levu, Rabi, and Taveuni
16°59′S 180°0′E Pacific Ocean Passing just east of the island of Moala,  Fiji (at 18°33′S 179°57′E)
Passing just west of the island of Totoya,  Fiji (at 19°0′S 179°52′W)
Passing just east of the island of Matuku,  Fiji (at 19°10′S 179°47′E)
60°0′S 180°0′E Southern Ocean
78°13′S 180°0′E Antarctica Ross Dependency, claimed by  New Zealand
90°0′S 180°0′E Antarctica Amundsen–Scott South Pole Station, South Pole
180° Meridian, Taveuni, Fiji

The meridian also passes between (but not particularly close to):

The only places where roads cross this meridian are in Fiji and Russia. Fiji has several such roads and some buildings very close to it. Russia has three roads in the Chukotka Autonomous Okrug.


Software representation problems

Many geographic software libraries or data formats project the world to a rectangle; very often this rectangle is split exactly at the 180th meridian. This often makes it non-trivial to do simple tasks (like representing an area, or a line) over the 180th meridian. Some examples:

  • The GeoJSON specification strongly suggests splitting geometries so that neither of their parts cross the antimeridian.[2]
  • In OpenStreetMap, areas (like the boundary of Russia) are split at the 180th meridian.

See also

Notes
  1. The word antimeridian can also mean the meridian opposite to any given meridian. E.g. 20° west is the antimeridian of 160° east.
  2. Butler, H.; Daly, M.; Doyle, A.; Gillies, S.; Hagen, S.; Schaub, T. (2016). RFC 7946 – The GeoJSON Format. sec. 3.1.9. doi:10.17487/RFC7946. RFC 7946.
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