# Geographic references

Map of Earth showing lines of latitude (horizontally) and longitude (vertically), Eckert VI projection; [https://www.cia.gov/library/publications/the-world-factbook/reference_maps/pdf/political_world.pdf large version] (pdf, 1.8MB)

A geographic coordinate system enables every location on the earth to be specified by the three coordinates of a spherical coordinate system aligned with the spin axis of the Earth.

## First and second dimensions: latitude and longitude

Borrowing from theories of the ancient Babylonians, later expanded by the famous Greek thinker and geographer Ptolemy, a full circle is divided into 360 degrees (360Â°).
• latitude (abbreviation: Lat.) is the angle at the centre of the coordinate system between any point on the earth's surface and the plane of the equator. Lines joining points of the same latitude are called parallels, and they trace concentric circles on the surface of the earth. Each pole is 90 degrees: the north pole 90Â° N; the south pole 90Â° S. The 0Â° parallel of latitude is designated the equator, an imaginary line that divides the globe into the Northern and Southern Hemispheres.
• longitude (abbreviation: Long.) is the angle east or west, at the centre of the coordinate system, between any point on the earth's surface and the plane of an arbitrary north-south line between the two geographical poles. Lines joining points of the same longitude are called meridians. All meridians are halves of great circles, and are not parallel: by definition they converge at the north and south poles. The line passing through the (former) Royal Observatory, Greenwich (near London in the UK) is the international zero-longitude reference line, the Prime Meridian. The antipodal meridian of Greenwich is both 180Â°W and 180Â°E.
By combining these two angles, the horizontal position of any location on Earth can be specified.

For example, Baltimore, Maryland (in the USA) has a latitude of 39.3Â° North, and a longitude of 76.6Â° West (). So, a vector drawn from the center of the earth to a point 39.3Â° north of the equator and 76.6Â° west of Greenwich will pass through Baltimore.

This latitude/longitude "webbing" is known as the common graticule. There is also a complementary transverse graticule (meaning the graticule is shifted 90Â°, so that the poles are on the horizontal equator), upon which all spherical trigonometry is ultimately based.

Traditionally, degrees have been divided into minutes (1/60th of a degree, designated by ′ or "m") and seconds (1/60th of a minute, designated by ″ or "s"). There are several formats for degrees, all of them appearing in the same Lat-Long order:
• DMS Degree:Minute:Second (49Â°30'00"-123d30m00s)
• DM Degree:Minute (49Â°30.0'-123d30.0m)
• DD Decimal Degree (49.5000Â°-123.5000d), generally with 4 decimal numbers.
To convert from DM or DMS to DD, decimal degrees = whole number of degrees, plus minutes divided by 60, plus seconds divided by 3600. DMS is the most common format, and is standard on all charts and maps, as well as global positioning systems and geographic information systems.

On a spherical surface at sea level, one latitudinal second measures 30.82 metres and one latitudinal minute 1849 metres. Parallels are each 110.9 kilometres away. The circles of longitude, the meridians, meet at the geographical poles, with the west-east width of a second being dependent on the latitude. On a spherical surface at sea level, one longitudinal second measures 30.92 metres on the equator, 26.76 metres on the 30th parallel, 19.22 metres in Greenwich (51Â° 28' 38" N) and 15.42 metres on the 60th parallel.

The width of one longitudinal degree on latitude can be calculated by this formula (to get the width per minute and second, divide by 60 and 3600, respectively):

::::
where Earth's average meridional radius approximately equals 6,367,449 m. Due to the average radius value used, this formula is of course not precise due to Earth's flattening. You can get real width of a longitudinal degree on latitude by:

:
where Earth's equatorial and polar radii, equal 6,378,137 m, 6,356,752.3 m, respectively.

The equator is the fundamental plane of all geographic coordinate systems. All spherical coordinate systems define such a fundamental plane.

Latitude and longitude values can be based on several different geodetic systems or datums, the most common being the WGS 84 used by all GPS equipment. In other words, the same point on the earth’s surface can be described by different latitude and longitude values depending on the reference datum.

In popular GIS software, data projected in latitude/longitude is often specified via a 'Geographic Coordinate System'. For example, data in latitude/longitude with the datum as the North American Datum of 1983 is denoted by 'GCS_North_American_1983'.

## Third dimension: altitude, height, depth

To completely specify a location on, in, or above the earth, one has to also specify the elevation, defined as the vertical position of the location relative to the centre of the reference system or some definition of the earth's surface. This is expressed in terms of the vertical distance to the earth below, but, because of the ambiguity of "surface" and "vertical", is more commonly expressed relative to a more precisely defined datum such as mean sea level (more precisely named geoid, a surface of constant gravity potential). The distance to the earth's center can be used both for very deep positions and for positions in space.

Other terms used with respect to the distance of a point from the earth's surface or some other datum are altitude, height, and depth.

## Geostationary coordinates

Geostationary satellites (e.g., television satellites ) are over the equator. So, their position related to Earth is expressed in longitude degrees. Their latitude does not change, and is always zero over the equator.

## External links

EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001. Their greatest hit, their debut single "time after time", peaked at #13 in the Oricon singles chart.
..... Click the link for more information.
Ancient Mesopotamia

Euphrates Tigris
Cities / Empires
Sumer: Uruk ' Ur ' Eridu
Kish ' Lagash ' Nippur
Akkadian Empire: Akkad
Babylon ' Isin ' Susa
Assyria: Assur Nineveh
..... Click the link for more information.
The term ancient Greece refers to the periods of Greek history in Classical Antiquity, lasting ca. 750 BC[1] (the archaic period) to 146 BC (the Roman conquest). It is generally considered to be the seminal culture which provided the foundation of Western Civilization.
..... Click the link for more information.
Claudius Ptolemaeus (Greek: Κλαύδιος Πτολεμαῖος; after 83 – 161 AD), known in English as Ptolemy, was a Greek[1] or Egyptian
..... Click the link for more information.
degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by Â° (the degree symbol), is a measurement of plane angle, representing 1360 of a full rotation.
..... Click the link for more information.
equator divides the planet into a Northern Hemisphere and a Southern Hemisphere, and has a latitude of 0. Latitude, usually denoted symbolically by the Greek letter phi, , gives the location of a place on Earth north or south of the equator.
..... Click the link for more information.
equator is an imaginary line on the Earth's surface equidistant from the North Pole and South Pole. It thus divides the Earth into a Northern Hemisphere and a Southern Hemisphere. The equators of other planets and astronomical bodies are defined analogously.
..... Click the link for more information.
equator divides the planet into a Northern Hemisphere and a Southern Hemisphere, and has a latitude of 0. On the Earth, a circle of latitude is an imaginary east-west circle connecting all locations that have a given latitude.
..... Click the link for more information.
This article or section is in need of attention from an expert on the subject.
Please help recruit one or [ improve this article] yourself. See the talk page for details.
..... Click the link for more information.
North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is, subject to the caveats explained below, defined as the point in the northern hemisphere where the Earth's axis of rotation meets the Earth's surface.
..... Click the link for more information.
South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is the southernmost point on the surface of the Earth. It lies on the continent of Antarctica, on the opposite side of the Earth from the North Pole.
..... Click the link for more information.
equator divides the planet into a Northern Hemisphere and a Southern Hemisphere, and has a latitude of 0. Longitude is the east-west geographic coordinate measurement most commonly utilized in cartography and global navigation.
..... Click the link for more information.
meridian (or line of longitude) is an imaginary arc on the Earth's surface from the North Pole to the South Pole that connects all locations with a given longitude. The position of a point on the meridan is given by the latitude.
..... Click the link for more information.
Royal Observatory, Greenwich (formerly the Royal Greenwich Observatory or RGO) was commissioned in 1675 by King Charles II, with the foundation stone being laid on 10 August.
..... Click the link for more information.
Motto
"Dieu et mon droit" [2]   (French)
"God and my right"
Anthem
"God Save the Queen" [3]
..... Click the link for more information.
Prime Meridian, also known as the International Meridian or Greenwich Meridian, is the meridian (line of longitude) passing through the Royal Greenwich Observatory in London — it is the meridian at which longitude is defined to be 0 degrees.
..... Click the link for more information.
antipodes (from Greek anti- "opposed" and pous "foot"; pronounced [Ã¦nˈtɪpəˌdiːz]) of any place on Earth is its antipodal point; that is, the region on the Earth's surface which is diametrically opposite to it.
..... Click the link for more information.
City of Baltimore
Downtown Baltimore

Flag
Seal
Nickname: Charm City,[1] Mob Town,[2][3] B-more, Crabtown, The City of Firsts
..... Click the link for more information.
Motto
"In God We Trust"   (since 1956)
"E Pluribus Unum"   ("From Many, One"; Latin, traditional)
Anthem
..... Click the link for more information.
Spherical trigonometry is a part of spherical geometry that deals with polygons (especially triangles) on the sphere and explains how to find relations between the involved angles.
..... Click the link for more information.
A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60) of one degree. [1] Since one degree is defined as one three hundred sixtieth (1/360) of a circle, 1 MOA is 1/21600 of the amount of arc in a closed circle, or
..... Click the link for more information.
A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60) of one degree. [1] Since one degree is defined as one three hundred sixtieth (1/360) of a circle, 1 MOA is 1/21600 of the amount of arc in a closed circle, or
..... Click the link for more information.
Decimal degrees (dd) are often used in Geographic Information Systems (GIS), web-mapping applications such as Google Maps, and GPS devices to express latitude and longitude coordinates, rather than expressing geographic coordinates with degrees, minutes, and seconds (dms).
..... Click the link for more information.
This article or section relies largely or entirely upon a .
Please help [ improve this article] by introducing appropriate of additional sources. ()
This article has been tagged since December 2006.
..... Click the link for more information.
1 metre =
SI units
1000 mm 0 cm
US customary / Imperial units
0 ft 0 in
The metre or meter[1](symbol: m) is the fundamental unit of length in the International System of Units (SI).
..... Click the link for more information.
equator divides the planet into a Northern Hemisphere and a Southern Hemisphere, and has a latitude of 0. On the Earth, a circle of latitude is an imaginary east-west circle connecting all locations that have a given latitude.
..... Click the link for more information.
1 kilometre =
SI units
0 m 0106 mm
US customary / Imperial units
0 ft 0 mi
A kilometre (American spelling: kilometer, symbol km
..... Click the link for more information.
meridian (or line of longitude) is an imaginary arc on the Earth's surface from the North Pole to the South Pole that connects all locations with a given longitude. The position of a point on the meridan is given by the latitude.
..... Click the link for more information.
This article or section is in need of attention from an expert on the subject.
Please help recruit one or [ improve this article] yourself. See the talk page for details.
..... Click the link for more information.
equator is an imaginary line on the Earth's surface equidistant from the North Pole and South Pole. It thus divides the Earth into a Northern Hemisphere and a Southern Hemisphere. The equators of other planets and astronomical bodies are defined analogously.
..... Click the link for more information.

This article is copied from an article on Wikipedia.org - the free encyclopedia created and edited by online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of the wikipedia encyclopedia articles provide accurate and timely information please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.