Editing Geographic coordinate system (section)

==Latitude and longitude==
[[File:Latitude_and_longitude_graticule_on_a_sphere.svg|thumb|upright=1.2|Diagram of the latitude {{mvar|ϕ}} and longitude {{mvar|λ}} angle measurements for a spherical model of the Earth.]]
{{Main|Latitude|Longitude}}

The ''latitude'' [[Phi|{{mvar|φ}}]] of a point on Earth's surface is defined in one of three ways, depending on the type of coordinate system. In each case, the latitude is the angle formed by the plane of the equator and a line formed by the point on the surface and a second point on equatorial plane. What varies between the types of coordinate systems is how the point on the equatorial plane is determined:
* In an astronomical coordinate system, the second point is found where the extension of the [[plumb bob]] vertical from the surface point intersects the equatorial plane.
* In a geodetic coordinate system, the second point is found where the [[normal vector]] from the surface of the ellipsoid at the surface point intersects the equatorial plane.
* In a geocentric coordinate system, the second point is the center of Earth.
The path that joins all points of the same latitude traces a circle on the surface of Earth, as viewed from above the north or south pole, called [[circle of latitude|parallels]], as they are parallel to the equator and to each other. The [[North Pole|north pole]] is 90°&nbsp;N; the [[South Pole|south pole]] is 90°&nbsp;S. The 0° parallel of latitude is defined to be the [[equator]], the [[fundamental plane (spherical coordinates)|fundamental plane]] of a geographic coordinate system. The equator divides the globe into [[Northern Hemisphere|Northern]] and [[Southern Hemisphere]]s.

The ''longitude'' [[lambda|{{mvar|λ}}]] of a point on Earth's surface is the angle east or west of a reference [[meridian (geography)|meridian]] to another meridian that passes through that point. All meridians are halves of great [[ellipse]]s, which converge at the North and South Poles. The meridian of the British [[Royal Observatory, Greenwich|Royal Observatory]] in [[Greenwich]], in southeast London, England, is the international [[prime meridian]], although some organizations—such as the French {{Lang|fr|[[Institut national de l'information géographique et forestière]]|italic=no}}—continue to use other meridians for internal purposes. The [[Antipodes|antipodal]] meridian of Greenwich is both 180°W and 180°E. This is not to be conflated with the [[International Date Line]], which diverges from it in several places for political and convenience reasons, including between far eastern Russia and the far western [[Aleutian Islands]].

The combination of these two components specifies the position of any location on the surface of Earth, without consideration of [[altitude]] or depth. The visual grid on a map formed by lines of latitude and longitude is known as a ''[[Graticule (cartography)|graticule]]''.<ref>{{cite book |url = https://books.google.com/books?id=jPVxSDzVRP0C&q=graticule&pg=PA224 |title=Glossary of the Mapping Sciences |last=American Society of Civil Engineers |date=1 January 1994 |publisher=ASCE Publications|isbn=9780784475706|language=en|page= 224 }}</ref> The origin/zero point of this system is located in the [[Gulf of Guinea]] about {{convert|625|km|sp=us|abbr=on|sigfig=2}} south of [[Tema]], Ghana, a location often facetiously called [[Null Island]].