Geographic coordinate system

Local datums chosen by a national cartographical organization include the

OSGB36

. Given a location, the datum provides the latitude ${\displaystyle \phi }$ and longitude ${\displaystyle \lambda }$. In the United Kingdom there are three common latitude, longitude, and height systems in use. WGS 84 differs at Greenwich from the one used on published maps OSGB36 by approximately 112 m. The military system

Points on the Earth's surface move relative to each other due to continental plate motion, subsidence, and diurnal

On the GRS 80 or WGS 84 spheroid at sea level at the Equator, one latitudinal second measures 30.715 m, one latitudinal minute is 1843 m and one latitudinal degree is 110.6 km. The circles of longitude, meridians, meet at the geographical poles, with the west–east width of a second naturally decreasing as latitude increases. On the Equator at sea level, one longitudinal second measures 30.92 m, a longitudinal minute is 1855 m and a longitudinal degree is 111.3 km. At 30° a longitudinal second is 26.76 m, at Greenwich (51°28′38″N) 19.22 m, and at 60° it is 15.42 m.

On the WGS 84 spheroid, the length in meters of a degree of latitude at latitude ϕ (that is, the number of meters you would have to travel along a north–south line to move 1 degree in latitude, when at latitude ϕ), is about

${\displaystyle 111132.92-559.82\,\cos 2\phi +1.175\,\cos 4\phi -0.0023\,\cos 6\phi }$^[12]

The returned measure of meters per degree latitude varies continuously with latitude.

Similarly, the length in meters of a degree of longitude can be calculated as

${\displaystyle 111412.84\,\cos \phi -93.5\,\cos 3\phi +0.118\,\cos 5\phi }$^[12]

(Those coefficients can be improved, but as they stand the distance they give is correct within a centimeter.)

The formulae both return units of meters per degree.

An alternative method to estimate the length of a longitudinal degree at latitude ${\displaystyle \phi }$ is to assume a spherical Earth (to get the width per minute and second, divide by 60 and 3600, respectively):

${\displaystyle {\frac {\pi }{180}}M_{r}\cos \phi \!}$

where Earth's average meridional radius ${\displaystyle \textstyle {M_{r}}\,\!}$ is 6,367,449 m. Since the Earth is an oblate spheroid, not spherical, that result can be off by several tenths of a percent; a better approximation of a longitudinal degree at latitude ${\displaystyle \phi }$ is

${\displaystyle {\frac {\pi }{180}}a\cos \beta \,\!}$

where Earth's equatorial radius ${\displaystyle a}$ equals 6,378,137 m and ${\displaystyle \textstyle {\tan \beta ={\frac {b}{a}}\tan \phi }\,\!}$; for the GRS 80 and WGS 84 spheroids, ${\textstyle {\tfrac {b}{a}}=0.99664719}$. (${\displaystyle \textstyle {\beta }\,\!}$ is known as the reduced (or parametric) latitude). Aside from rounding, this is the exact distance along a parallel of latitude; getting the distance along the shortest route will be more work, but those two distances are always within 0.6 m of each other if the two points are one degree of longitude apart.

Like any series of multiple-digit numbers, latitude-longitude pairs can be challenging to communicate and remember. Therefore, alternative schemes have been developed for encoding GCS coordinates into alphanumeric strings or words:

• the Maidenhead Locator System, popular with radio operators.
• the World Geographic Reference System (GEOREF), developed for global military operations, replaced by the current Global Area Reference System (GARS).
• Open Location Code or "Plus Codes", developed by Google and released into the public domain.
• Geohash, a public domain system based on the Morton Z-order curve.
• Mapcode, an open-source system originally developed at TomTom.
• What3words, a proprietary system that encodes GCS coordinates as pseudorandom sets of words by dividing the coordinates into three numbers and looking up words in an indexed dictionary.

These are not distinct coordinate systems, only alternative methods for expressing latitude and longitude measurements.

• Decimal degrees – Angular measurements, typically for latitude and longitude
• Geographical distance – Distance measured along the surface of the Earth
• Geographic information system – System to capture, manage, and present geographic data
• Geo URI scheme – System of geographic location identifiers
• ISO 6709, standard representation of geographic point location by coordinates
• Linear referencing – method of spatial referencingPages displaying wikidata descriptions as a fallback
• Primary direction
   – Celestial coordinate system used to specify the positions of celestial objectsPages displaying short descriptions of redirect targets
• Planetary coordinate system
  • Selenographic coordinate system
• Spatial reference system – System to specify locations on Earth
• Jan Smits (2015). Mathematical data for bibliographic descriptions of cartographic materials and spatial data. Geographical co-ordinates. ICA Commission on Map Projections.