Meridian ( geography ) - wikipedia Meridian ( geography ) For the astronomical concept, see Meridian ( astronomy ). For other uses, see Meridian. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( April 2012 ) A ( geographical ) meridian ( or line of longitude ) is the half of an imaginary great circle on the Earth 's surface, terminated by the North Pole and the South Pole, connecting points of equal longitude. The position of a point along the meridian is given by its latitude indicating how many degrees north or south of the Equator the point is. Each meridian is perpendicular to all circles of latitude. Each is also the same length, being half of a great circle on the Earth 's surface and therefore measuring 20,003.93 km ( 12,429.9 miles ). Contents 1 Etymology 2 Geographic 3 Magnetic 4 See also 5 References 6 External links Etymology The term `` meridian '' comes from the Latin meridies, meaning `` midday '' ; the sun crosses a given meridian midway between the times of sunrise and sunset on that meridian. The same Latin stem gives rise to the terms a.m. ( ante meridiem ) and p.m. ( post meridiem ) used to disambiguate hours of the day when utilizing the 12 - hour clock. Geographic The astronomic prime meridian at Greenwich, England. The geodetic prime meridian is actually 102.478 meters east of this point since the adoption of WGS84. The meridian through Greenwich ( inside Greenwich Park ), England, called the Prime Meridian, was set at zero degrees of longitude, while other meridians were defined by the angle at the center of the earth between where it and the prime meridian cross the equator. As there are 360 degrees in a circle, the meridian on the opposite side of the earth from Greenwich, the antimeridian, forms the other half of a circle with the one through Greenwich, and is at 180 ° longitude near the International Date Line ( with land mass and island deviations for boundary reasons ). The meridians from West of Greenwich ( 0 ° ) to the antimeridian ( 180 ° ) define the Western Hemisphere and the meridians from East of Greenwich ( 0 ° ) to the antimeridian ( 180 ° ) define the Eastern Hemisphere. Most maps show the lines of longitude. The position of the prime meridian has changed a few times throughout history, mainly due to the transit observatory being built next door to the previous one ( to maintain the service to shipping ). Such changes had no significant practical effect. Historically, the average error in the determination of longitude was much larger than the change in position. The adoption of WGS84 ( `` World Geodetic System 84 '' ) as the positioning system has moved the geodetic prime meridian 102.478 metres east of its last astronomic position ( measured at Greenwich ). The position of the current geodetic prime meridian is not identified at all by any kind of sign or marking ( as the older astronomic position was ) in Greenwich, but can be located using a GPS receiver. Magnetic The magnetic meridian is an equivalent imaginary line connecting the magnetic south and north poles and can be taken as the horizontal component of magnetic force lines along the surface of the earth. Therefore, a compass needle will be parallel to the magnetic meridian. The angle between the magnetic and the true meridian is the magnetic declination, which is relevant for navigating with a compass. See also Meridian ( astronomy ) Meridian arc Prime meridian Principal meridian Public Land Survey System, United States Dominion Land Survey, Canada References Jump up ^ `` Geomagnetism ''. met.gov.pk. Archived from the original on 22 June 2007. Retrieved 10 November 2008. Jump up ^ `` Magnetic meridian ''. Museo Galileo. Retrieved 12 September 2015. External links Wikimedia Commons has media related to Longitudes. The Principal Meridian Project ( US ) ( 1 ) Note : This is a large file, approximately 46MB. Searchable PDF prepared by the author, C.A. White. Resources page of the U.S. Department of the Interior, Bureau of Land Management `` Meridian ''. The New Student 's Reference Work. 1914. Circles of latitude / Meridians Equator Tropic of Cancer Tropic of Capricorn Arctic Circle Antarctic Circle Equator Tropic of Cancer Tropic of Capricorn Arctic Circle Antarctic Circle Equator Tropic of Cancer Tropic of Capricorn Arctic Circle Antarctic Circle W 0 ° E 30 ° 60 ° 90 ° 120 ° 150 ° 180 ° 30 ° 60 ° 90 ° 120 ° 150 ° 180 ° 5 ° 15 ° 25 ° 35 ° 45 ° 55 ° 65 ° 75 ° 85 ° 95 ° 105 ° 115 ° 125 ° 135 ° 145 ° 155 ° 165 ° 175 ° 5 ° 15 ° 25 ° 35 ° 45 ° 55 ° 65 ° 75 ° 85 ° 95 ° 105 ° 115 ° 125 ° 135 ° 145 ° 155 ° 165 ° 175 ° 10 ° 20 ° 40 ° 50 ° 70 ° 80 ° 100 ° 110 ° 130 ° 140 ° 160 ° 170 ° 10 ° 20 ° 40 ° 50 ° 70 ° 80 ° 100 ° 110 ° 130 ° 140 ° 160 ° 170 ° 0 ° 10 ° 20 ° 30 ° 40 ° 50 ° 60 ° 70 ° 80 ° 90 ° 10 ° 20 ° 30 ° 40 ° 50 ° 60 ° 70 ° 80 ° 90 ° 5 ° N 15 ° 25 ° 35 ° 45 ° 55 ° 65 ° 75 ° 85 ° 5 ° S 15 ° 25 ° 35 ° 45 ° 55 ° 65 ° 75 ° 85 ° 45x90 45x90 45x90 45x90 Retrieved from `` https://en.wikipedia.org/w/index.php?title=Meridian_(geography)&oldid=797135717 '' Categories : Surveying Lines of longitude Hidden categories : Articles needing additional references from April 2012 All articles needing additional references All accuracy disputes Articles with disputed statements from March 2012 Commons category with local link different than on Wikidata Wikipedia articles incorporating citation to the NSRW Wikipedia articles incorporating citation to the NSRW with an wstitle parameter Talk Contents About Wikipedia Afrikaans Asturianu Azərbaycanca বাংলা Bân - lâm - gú Башҡортса Беларуская Беларуская ( тарашкевіца ) ‎ Български Català Čeština Deutsch Dolnoserbski Eesti Ελληνικά Español Esperanto Estremeñu Euskara فارسی Français Frysk Gaeilge Galego 한국어 Հայերեն हिन्दी Hornjoserbsce Hrvatski Ilokano Bahasa Indonesia Italiano עברית Қазақша Кыргызча Latina Latviešu Lietuvių Lumbaart Magyar Македонски മലയാളം Bahasa Melayu Nederlands 日本 語 Occitan Олык марий ភាសា ខ្មែរ Polski Português Русиньскый Русский Саха тыла Simple English Slovenčina Slovenščina Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska Tagalog ไทย Українська اردو Tiếng Việt Winaray ייִדיש 中文 Edit links This page was last edited on 25 August 2017, at 04 : 41. 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Question: what is the imaginary line running north and south
Answer: (geographical) meridian