# Geographic coordinate system

Coordinatesgeographic coordinateslatitude and longitudegeographic coordinategeographic locationgeographical areaLocationgeographical coordinatesdecimal degree notationlongitude and latitude
A geographic coordinate system is a coordinate system that enables every location on Earth to be specified by a set of numbers, letters or symbols.wikipedia
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### Longitude

WestlongitudinalE
A common choice of coordinates is latitude, longitude and elevation.
Longitude (, AU and UK also ), is a geographic coordinate that specifies the east–west position of a point on the Earth's surface, or the surface of a celestial body.

### Latitude

latitudesSouthlatitudinal
A common choice of coordinates is latitude, longitude and elevation.
In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earth's surface.

### Horizontal position representation

Horizontal positionhorizontal gridrepresentation
The coordinates are often chosen such that one of the numbers represents a vertical position and two or three of the numbers represent a horizontal position; alternatively, a geographic position may be expressed in a combined three-dimensional Cartesian vector.
It is a type of geographic coordinate system.

### Prime meridian

GreenwichGreenwich meridianGreenwich Prime Zero meridian
In the 1st or 2nd century, Marinus of Tyre compiled an extensive gazetteer and mathematically-plotted world map using coordinates measured east from a prime meridian at the westernmost known land, designated the Fortunate Isles, off the coast of western Africa around the Canary or Cape Verde Islands, and measured north or south of the island of Rhodes off Asia Minor.
A prime meridian is a meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°.

### Map projection

projectionequal-areacartographic projection
To specify a location on a plane requires a map projection.
Therefore, in geoidal projections that preserve such properties, the mapped graticule would deviate from a mapped ellipsoid's graticule.

### Geographic coordinate conversion

datum transformationheretransform
Converting coordinates from one datum to another requires a datum transformation such as a Helmert transformation, although in certain situations a simple translation may be sufficient.
In geodesy, conversion among different geographic coordinate systems is made necessary by the different geographic coordinate systems in use across the world and over time.

### Coordinate system

coordinatescoordinateaxis
A geographic coordinate system is a coordinate system that enables every location on Earth to be specified by a set of numbers, letters or symbols.

### South Pole

90Geographic South PoleSouth
The North Pole is 90° N; the South Pole is 90° S. The 0° parallel of latitude is designated the Equator, the fundamental plane of all geographic coordinate systems.
The geographic coordinates of the South Pole are usually given simply as 90°S, since its longitude is geometrically undefined and irrelevant.

### Hipparchus

HipparchosHipparchus of NicaeaHipparchus of Nicea
A century later, Hipparchus of Nicaea improved on this system by determining latitude from stellar measurements rather than solar altitude and determining longitude by timings of lunar eclipses, rather than dead reckoning.
It seems he did not introduce many improvements in methods, but he did propose a means to determine the geographical longitudes of different cities at lunar eclipses (Strabo Geographia 1 January 2012).

### Geography (Ptolemy)

GeographyGeographiaPtolemy
Ptolemy's 2nd-century Geography used the same prime meridian but measured latitude from the Equator instead.
The world map from the 11th-century Book of Curiosities is the earliest surviving map of the Muslim or Christian worlds to include a graticule but the copyist seems to have not understood its purpose, starting it from the left using twice the intended scale and then (apparently realizing his mistake) giving up halfway through.

### Antipodes

antipodeantipodalAntipodean
The antipodal meridian of Greenwich is both 180°W and 180°E.
If the geographic coordinates (latitude and longitude) of a point on the Earth's surface are, then the coordinates of the antipodal point are (−φ, θ ± 180°).

### Fundamental plane (spherical coordinates)

fundamental planefundamental planes
The North Pole is 90° N; the South Pole is 90° S. The 0° parallel of latitude is designated the Equator, the fundamental plane of all geographic coordinate systems.

### Universal Transverse Mercator coordinate system

UTMUniversal Transverse MercatorUTM Grid
Common map projections in current use include the Universal Transverse Mercator (UTM), the Military Grid Reference System (MGRS), the United States National Grid (USNG), the Global Area Reference System (GARS) and the World Geographic Reference System (GEOREF).
The Universal Transverse Mercator (UTM) is a system for assigning coordinates to locations on the surface of the Earth.

### ECEF

Earth-centered, Earth-fixedEarth-centered Earth-fixedgeocenter
The Earth-centered Earth-fixed (also known as the ECEF, ECF, or conventional terrestrial coordinate system) rotates with the Earth and has its origin at the center of the Earth.
ECEF (acronym for earth-centered, earth-fixed), also known as ECR (initialism for earth-centered rotational), is a geographic and Cartesian coordinate system and is sometimes known as a "conventional terrestrial" system.

### United States National Grid

National GridUSNG
Common map projections in current use include the Universal Transverse Mercator (UTM), the Military Grid Reference System (MGRS), the United States National Grid (USNG), the Global Area Reference System (GARS) and the World Geographic Reference System (GEOREF).
While latitude and longitude are well suited to describing locations over large areas of the Earth's surface, most practical land navigation situations occur within much smaller, local areas.

### Decimal degrees

decimalisation of circular measure
Decimal degrees (DD) express latitude and longitude geographic coordinates as decimal fractions and are used in many geographic information systems (GIS), web mapping applications such as OpenStreetMap, and GPS devices.

### Figure of the Earth

curvature of the Earthshape of the EarthEarth's curvature
Oblate ellipsoids have constant radius of curvature east to west along parallels, if a graticule is drawn on the surface, but varying curvature in any other direction.

### Vertical position

depthvertical coordinatevertical distance
The coordinates are often chosen such that one of the numbers represents a vertical position and two or three of the numbers represent a horizontal position; alternatively, a geographic position may be expressed in a combined three-dimensional Cartesian vector.

### Linear referencing

Linear Reference Systemlinear referencing systemreference points
Coordinates such as latitude and longitude are another member of the family, as are landmark references such as "5 km south of Ayers Rock."

### Map

Mapspolitical mapelectronic map
To establish the position of a geographic location on a map, a map projection is used to convert geodetic coordinates to plane coordinates on a map; it projects the datum ellipsoidal coordinates and height onto a flat surface of a map.

### N-vector

n''-vectorEllipsoid normal vectorgeodetic normal
The coordinates are often chosen such that one of the numbers represents a vertical position and two or three of the numbers represent a horizontal position; alternatively, a geographic position may be expressed in a combined three-dimensional Cartesian vector.

### Elevation

hightopographic elevationelevated
A common choice of coordinates is latitude, longitude and elevation.

### Invention

inventorinventionsinventors
The invention of a geographic coordinate system is generally credited to Eratosthenes of Cyrene, who composed his now-lost Geography at the Library of Alexandria in the 3rd century BC.

### Cyrene, Libya

CyreneCyrenaeanArchaeological Site of Cyrene
The invention of a geographic coordinate system is generally credited to Eratosthenes of Cyrene, who composed his now-lost Geography at the Library of Alexandria in the 3rd century BC.