# Encyclopedia

"Graticule" redirects here and may mean: a wire or cross lines in an optical focusing system.[[File:WorldMapLongLat-eq-circles-tropics-non.png|thumb|440px|Map of Earth showing lines of latitude (horizontally) and longitude (vertically), Eckert VI projection; [https://www.cia.gov/library/publications/the-world-factbook/graphics/ref_maps/pdf/political_world.pdf large versiom is a coordinate system that enables every location on Earth to be specified in three coordinates, using mainly a spherical coordinate system.
.The Earth is not a sphere, but an irregular shape approximating an ellipsoid; the challenge is to define a coordinate system that can accurately state each topographical point as an unambiguous tuple of numbers.^ Coordinate System A reference system for defining precise locations on the Earth's surface.
• 07a Geographic Reference Systems 11 January 2010 7:50 UTC www.microimages.com [Source type: Reference]

^ The WGS84 geographic coordinate system defines ellipsoidal coordinates over the standard WGS84 ellipsoid.
• Converting Coordinates Between Coordinate Systems 22 September 2009 20:29 UTC www.ilog.com [Source type: Reference]

^ The State Plane system also defines both projection and coordinate system.
• Projections and Coordinate Systems 11 January 2010 7:50 UTC courses.washington.edu [Source type: FILTERED WITH BAYES]

[1]

## Latitude and longitude

Latitude phi (φ) and Longitude lambda (λ)
.Latitude (abbreviation: Lat., φ, or phi) is the ace to the equatorial plane, measured from the center of the sphere.^ A great circle is a circle where a plane, which goes through the center of the sphere, intersects the sphere.

^ Great circle: The intersection between a sphere and a plane passing through the center of the sphere.

^ A small circle is produced by passing a plane through any part of the sphere other than the center.
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

.Lines joining points of the same latitude are called parallels, which trace concentric circles on the surface of the Earth, parallel to the equator.^ Parallels of latitude are all small circles, except for the equator.
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

^ Parallels are lines which circle the earth and are perpendicular to its axis, the equator is the longest of these lines.

^ The point on the Earth surface directly below a given point above the surface is not on a line joining the given point and the centre of the Earth.
• Background: Coordinate systems and transformations 11 January 2010 7:50 UTC www.spenvis.oma.be [Source type: Academic]

.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 equator is designated as having a Northing value of 0 for northern hemisphere coordinates.
• The GIS Primer - Nature of Geographic Information 11 January 2010 7:50 UTC www.innovativegis.com [Source type: Reference]

^ Parallels of latitude are all small circles, except for the equator.
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

^ Projection projection projection Projection from geographic to projected coordinate system.

.The equator divides the globe into Northern and Southern Hemispheres.^ The equator divides the earth into northern and southern hemispheres.

^ The world is divided into 60 zones in the Northern Hemisphere and 60 corresponding zones in the southern hemisphere.

^ The equator is designated as having a Northing value of 0 for northern hemisphere coordinates.
• The GIS Primer - Nature of Geographic Information 11 January 2010 7:50 UTC www.innovativegis.com [Source type: Reference]

.Longitude (abbreviation: Long., λ, or lambda) is the angle east or west of a reference meridian between the two geographical poles to another meridian that passes through an arbitrary point.^ The geodetic longitude of a point is the angle between a reference plane and a plane passing through the point, both planes being perpendicular to the equatorial plane.
• Coordinate Systems Overview 11 January 2010 7:50 UTC www.colorado.edu [Source type: Reference]

^ Longitude indicates the number of degrees east or west of the prime meridian (0 degrees).
• File 89, GeoRef: Geographic Coordinates Fields 11 January 2010 7:50 UTC support.dialog.com [Source type: Reference]

^ Longitude 1 is east of the prime meridian and Longitude 2 is west.
• File 89, GeoRef: Geographic Coordinates Fields 11 January 2010 7:50 UTC support.dialog.com [Source type: Reference]

.All meridians are halves of great circles, and are not parallel.^ Half circles from pole to pole, which are all perpendicular to the equatorialplane, are called meridians .
• Astronomical Coordinate Systems 11 January 2010 7:50 UTC www.seds.org [Source type: FILTERED WITH BAYES]

^ Parallels of latitude are all small circles, except for the equator.
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

^ A great circle, formed by passing a plane through the center of a sphere, divides the sphere into two equal halves.
• Astronomy Supplement - Astronomical Coordinate Systems and Time Systems 11 January 2010 7:50 UTC physics.gmu.edu [Source type: FILTERED WITH BAYES]

.They converge at the north and south poles.^ Your choices are North Pole and South Pole.
• 07a.2 Coordinate System and Projection Parameters 11 January 2010 7:50 UTC www.microimages.com [Source type: Reference]

^ Note how the meridians converge at both the North and South Poles.
• GEO327G/386G  Lab 2 - Map Projections and Coordinate Systems 11 January 2010 7:50 UTC www.geo.utexas.edu [Source type: FILTERED WITH BAYES]
• Geol 2161  Lab 2 - Map Projections and Coordinate Systems 11 January 2010 7:50 UTC cda.morris.umn.edu [Source type: FILTERED WITH BAYES]

^ (Lat/Long) The fundamental geographic coordinate system, consisting of parallel lines of latitude circling the globe in an east-west direction and north-south lines of longitude (meridians) that converge at the poles.
• Geographic Information Systems Introduction 11 January 2010 7:50 UTC www.gis.state.mn.us [Source type: Reference]

.A line passing to the rear of the Royal Observatory, Greenwich (near London in the UK) has been chosen as the international zero-longitude reference line, the Prime Meridian.^ The line of zero longitude is called the prime meridian.
• Coordinate systems, map projections, and geographic (datum) transformations 11 January 2010 7:50 UTC edndoc.esri.com [Source type: Reference]

^ For most GCSs, the prime meridian is the longitude that passes through Greenwich, England.
• Coordinate systems, map projections, and geographic (datum) transformations 11 January 2010 7:50 UTC edndoc.esri.com [Source type: Reference]

^ The line of longitude corresponding to 0º, which passes through Greenwich in London, is called the Prime (or Greenwich) Meridian.
• BBC/OU Open2.net - Mathematical Thinking - Measuring latitude and longitude 25 September 2009 5:27 UTC www.open2.net [Source type: General]

.Places to the east are in the eastern hemisphere, and places to the west are in the western hemisphere.^ Longitudes in the western hemisphere must be either demarcated with a negative sign (i.e., as negative degrees of longitude) or explicitly stated as "west longitude" or "degrees west."

^ The longitude of a place is the number of degrees that it is east or west of Greenwich, England.

^ Astronomers use a similar coordinate system to describe positions on other planets, but do not try to deal with eastern and western hemispheres; instead they divide the planet into 360 degrees and measure positions going west from the 0 meridian.

The antipodal meridian of Greenwich is both 180°W and 180°E.
.In 1884, the United States hosted the International Meridian Conference and twenty-five nations attended.^ Outside the United States, please direct all inquiries to your local ESRI International Distributor.
• U.S. Geographic Names Information System School 11 January 2010 7:50 UTC www.leo.lehigh.edu [Source type: Reference]

^ National atlas of the United States "The National Atlas of the United States of America will include four distinct products.
• By Subject - Maps/Geographic Information Systems - Maps 11 January 2010 7:50 UTC www.lib.washington.edu [Source type: Reference]

^ National Atlas of the United States of America-- 1870, 1880, 1890, and 1970 editions These digitized 1870, 1880, 1890, and 1970 editions of the National Atlas is on the Library of Congress American Memory Web site.
• Geographic Links A-G 11 January 2010 7:50 UTC www4.uwm.edu [Source type: Academic]

.Twenty-two of them agreed to adopt the location of Greenwich as the zero-reference line.^ Under the null hypothesis of no relationship between geographic location and genetic similarity, all points would be on the zero line.
• PLoS ONE: Spatiotemporal Structure of Molecular Evolution of H5N1 Highly Pathogenic Avian Influenza Viruses in Vietnam 11 January 2010 7:50 UTC www.plosone.org [Source type: Academic]

^ The datum defines the origin and orientation of lines of latitude and longitude, and is a "starting point" of reference for measuring locations on the surface of the earth.
• Geographic and Projected Coordinate Systems - Keys to Creating and Understanding Maps 11 January 2010 7:50 UTC www.fgdl.org [Source type: FILTERED WITH BAYES]

^ The zero point for these lines is the prime meridian which runs through Greenwich, England.

San Domingo voted against the adoption of that motion, while France and Brazil abstained.[2] .To date, there exist organizations around the world which continue using historical prime meridians before the acceptance of Greenwich and the ill-attended conference became common-place.^ Sometimes no transformation exists, or you have to use a third GCS like the World Geodetic System 1984 (WGS84) and combine two transformations.
• Coordinate systems, map projections, and geographic (datum) transformations 11 January 2010 7:50 UTC edndoc.esri.com [Source type: Reference]

^ They are numbered using degrees beginning at the Royal Greenwich Observatory in England, which is designated as 0°, and continue both East and West until they meet at 180°.
• Geoscience Australia: Geodesy - Datums and Coordinates 11 January 2010 7:50 UTC www.ga.gov.au [Source type: Reference]

^ Around 50 years later, a greek, Hipparchus of Rhodes invented a world-wide referencing system of meridians and paralells that we use to describe earth locations: latitude and longitude.
• Understanding Coordinate Systems 11 January 2010 7:50 UTC www.gsd.harvard.edu [Source type: FILTERED WITH BAYES]

[3]
.The combination of these two components specifies the position of any location on the planet, but does not consider altitude nor depth.^ There are two components to positional accuracy.
• The GIS Primer - Nature of Geographic Information 11 January 2010 7:50 UTC www.innovativegis.com [Source type: Reference]

^ By combining these two angles, the position of any location on Earth can be specified.
• Remath - Pedagogical Plan 11 January 2010 7:50 UTC remath.itd.cnr.it [Source type: FILTERED WITH BAYES]

^ Most state DOTs have devoted considerable effort to developing, maintaining, and updating these two components.

.For example, Baltimore, Maryland (in the USA) has a latitude of 39.3° North, and a longitude of 76.6° West.^ Lines of latitude run east-west but north-south distances are measured between them.
• Use of Geographic Coordinates to Pinpoint Location in Map Reading 11 January 2010 7:50 UTC www.map-reading.com [Source type: FILTERED WITH BAYES]
• Orienteering - Geographic Coordinates 11 January 2010 7:50 UTC www.4orienteering.com [Source type: FILTERED WITH BAYES]
• SurvivalIQ Handbook: Land Navigation - Grids - Geographic coordinates 11 January 2010 7:50 UTC www.survivaliq.com [Source type: Reference]

^ The Equirectangular coordinate system is essentially a direct scaling of longitudes and latitudes to distances east and north, with the scaling selected such that distortion is minimized along the central latitude parallel.
• NMPlot User's Guide, Chapter 20: Geographic Coordinate Systems 11 January 2010 7:50 UTC www.wasmerconsulting.com [Source type: Reference]

^ This unit provides an overview of latitude and longitude, including: Earth rotation, the North and South Poles, and the Equator Parallels of latitude and meridians of longitude Determination of north or south position with latitude The use of longitude to determine east or west position The measurement of latitude and longitude with degrees, minutes, and seconds Learning Outcomes .
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

.So, a vector drawn from the center of the Earth to a point 39.3° north of the equator and 76.6° west of Greenwich will pass through Baltimore.^ The geodetic longitude of a point is the angle between a reference plane and a plane passing through the point, both planes being perpendicular to the equatorial plane.
• Coordinate Systems Overview 11 January 2010 7:50 UTC www.colorado.edu [Source type: Reference]

^ The latitude measurement of the Earth is based on 0 to 90 degrees of height (latitude) north and south of the equator.
• Communications device for conveying geographic location information over capacity constrained wireless systems - Patent 7272494 11 January 2010 7:50 UTC www.freepatentsonline.com [Source type: Reference]

^ Earth and the meridian of Greenwich (UK) which is the international zero-longitude point (longitude=0 degrees).
• Remath - Pedagogical Plan 11 January 2010 7:50 UTC remath.itd.cnr.it [Source type: FILTERED WITH BAYES]

.This latitude/longitude "webbing" is known as the conjugate graticule.^ These are data with known latitude, longitude, and elevation, or other horizontal and vertical coordinates.
• Down to Earth: Geographical Information for Sustainable Development in Africa 11 January 2010 7:50 UTC www.nap.edu [Source type: Academic]

^ The geometries are then transformed using the coordinate system whose SRID is 8199 and whose well-known name is "Longitude / Latitude (Arc 1950)".
• 6 Coordinate Systems (Spatial Reference Systems) 11 January 2010 7:50 UTC download.oracle.com [Source type: Reference]
• Coordinate Systems (Spatial Reference Systems) 11 January 2010 7:50 UTC download.oracle.com [Source type: Reference]

^ Software that converts between UTM and latitude-longitude can be found on the web (see the references).

.In defining an ellipse, the short (vertical) diameter is known as the conjugate diameter, and the long (horizontal) diameter — perpendicular, or "transverse", to the conjugate — is the transverse diameter.^ These are data with known latitude, longitude, and elevation, or other horizontal and vertical coordinates.
• Down to Earth: Geographical Information for Sustainable Development in Africa 11 January 2010 7:50 UTC www.nap.edu [Source type: Academic]

^ A set of points on the ground whose horizontal and vertical location is known.
• GIS GLOSSARY 11 January 2010 7:50 UTC volusia.org [Source type: Reference]

^ Control Points: A set of points on the ground whose horizontal and vertical location is known.

[4] .With a sphere or ellipsoid, the conjugate diameter is known as the polar axis and the transverse as the equatorial axis.^ Semi-major Axis -- radius of the equatorial axis of the ellipsoid.
• 4 : Spatial Reference Information — Federal Geographic Data Committee 11 January 2010 7:50 UTC www.fgdc.gov [Source type: Reference]

^ Ellipsoidal models define an ellipsoid with an equatorial radius and a polar radius.
• Coordinate Systems Overview 11 January 2010 7:50 UTC www.colorado.edu [Source type: Reference]

^ Mathematically, the reference ellipsoid is an oblate (flattened) ellipsoid of revolution with two different axes, an equatorial semi-major axis a and a polar semi-minor axis b .
• Coordinate Reference Systems and Positioning - Wikibooks, collection of open-content textbooks 11 January 2010 7:50 UTC en.wikibooks.org [Source type: Reference]

.The graticule perspective is based on this designation: As the longitudinal rings — geographically defined, all great circles — converge at the poles, it is the poles that the conjugate graticule is defined.^ The arc is based on a great circle.
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

^ (Lat/Long) The fundamental geographic coordinate system, consisting of parallel lines of latitude circling the globe in an east-west direction and north-south lines of longitude (meridians) that converge at the poles.
• Geographic Information Systems Introduction 11 January 2010 7:50 UTC www.gis.state.mn.us [Source type: Reference]

^ Half circles from pole to pole, which are all perpendicular to the equatorialplane, are called meridians .
• Astronomical Coordinate Systems 11 January 2010 7:50 UTC www.seds.org [Source type: FILTERED WITH BAYES]

.If the polar vertex is "pulled down" 90°, so that the vertex is on the equator, or transverse diameter, then it becomes the transverse graticule, upon which all spherical trigonometry is ultimately based (if the longitudinal vertex is between the poles and equator, then it is considered an oblique graticule).^ The latitude measurement of the Earth is based on 0 to 90 degrees of height (latitude) north and south of the equator.
• Communications device for conveying geographic location information over capacity constrained wireless systems - Patent 7272494 11 January 2010 7:50 UTC www.freepatentsonline.com [Source type: Reference]

^ At the equator the diameter of the earth is 7927 miles; at the poles, it is very close to 7900 miles.
• Geographic and Projected Coordinate Systems - Keys to Creating and Understanding Maps 11 January 2010 7:50 UTC www.fgdl.org [Source type: FILTERED WITH BAYES]

^ Distortion is severe near the poles of the normal aspect or 90° from the central line in the transverse and oblique aspects.
• Projections and Coordinate Systems 11 January 2010 7:50 UTC courses.washington.edu [Source type: FILTERED WITH BAYES]

### Degrees: a measurement of angle

.There are several formats for writing degrees, all of them appearing in the same Lat, Long order.^ So long as we are doing "pure" CAD, the only thing that matters is that the scale is accurate and that all the drawings are based on the same common position of the X, Y origin.
• Coordinates Tutorial 11 January 2010 7:50 UTC demo.manifold.net [Source type: FILTERED WITH BAYES]

^ Calculations are based on the same degree of imprecision in both coordinates and are given for several different latitudes.
• MaNIS/HerpNet/ORNIS Georeferencing Guidelines 11 January 2010 7:50 UTC manisnet.org [Source type: Reference]

^ There appears to be a religious theme to 32.7 degrees.
• Patterns of geographic coordinates - A New Age / Bible Prophecy Discussion 22 September 2009 20:29 UTC www.revelation13.net [Source type: FILTERED WITH BAYES]
• Patterns of geographic coordinates - A New Age / Bible Prophecy Discussion 22 September 2009 20:29 UTC www.angelfire.com [Source type: FILTERED WITH BAYES]

• DMS Degrees:Minutes:Seconds (49°30'00"N, 123°30'00"W)
• DM Degrees:Decimal Minutes (49°30.0', -123°30.0'), (49d30.0m,-123d30.0')
• DD Decimal Degrees (49.5000°,-123.5000°), generally with 4-6 decimal numbers.

## Geodesic height

.To completely specify a location of a topographical feature on, in, or above the Earth, one has to also specify the vertical distance from the centre of the sphere, or from the surface of the sphere.^ Locating map features correctly in relation to their actual locations on the surface of the earth.
• Geographic Information Systems Introduction 11 January 2010 7:50 UTC www.gis.state.mn.us [Source type: Reference]

^ The best of these models can represent the shape of the earth over the smoothed, averaged sea-surface to within about one-hundred meters.
• Coordinate Systems Overview 11 January 2010 7:50 UTC www.colorado.edu [Source type: Reference]

^ However, the celestial sphere, which is the apparent sphere of the sky, is not a plane: It is the inside of a sphere, and one that rotates relative to Earth's surface.
• Astronomy Supplement - Astronomical Coordinate Systems and Time Systems 11 January 2010 7:50 UTC physics.gmu.edu [Source type: FILTERED WITH BAYES]

.Because of the ambiguity of "surface" and "vertical", it is more commonly expressed relative to a more precisely defined vertical datum such as mean sea level at a named point.^ The geoid is a gravity surface approximating mean sea level.
• Geographic Coordinate System Transformations 11 January 2010 7:50 UTC www.posc.org [Source type: Academic]

^ The name of the vertical datum (geoid).
• GeoVRML 1.0 - Nodes 11 January 2010 7:50 UTC www.ai.sri.com [Source type: Reference]

^ The coordinate system in which the time datum is defined as the vertical reference.
• Entity COORDINATE_SYSTEM in Schema Seabed 11 January 2010 7:50 UTC www.ocean.slb.com [Source type: Reference]

Each country has defined its own datum. .For example, in the United Kingdom the reference point is Newlyn.^ The communications unit of claim 1, wherein the geographic area is independent of a fixed geographic reference point.
• Communications device for conveying geographic location information over capacity constrained wireless systems - Patent 7272494 11 January 2010 7:50 UTC www.freepatentsonline.com [Source type: Reference]

^ Grids - Reference system - Geographic coordinates - Military grids - United states army military grid reference system - Locate a point using grid coordinates - Locate a point using the us army military grid reference system - Grid reference box - Other grid systems - Protection of map coordinates and locations 5.
• SurvivalIQ Handbook: Land Navigation - Grids - Geographic coordinates 11 January 2010 7:50 UTC www.survivaliq.com [Source type: Reference]

^ The communications unit of claim 12, wherein the geographic area is independent of a fixed geographic reference point.
• Communications device for conveying geographic location information over capacity constrained wireless systems - Patent 7272494 11 January 2010 7:50 UTC www.freepatentsonline.com [Source type: Reference]

.The distance to Earth's centre can be used both for very deep positions and for positions in space.^ Their uses include comparing positions, calculating distances, and general assistance in navigating from one point or place to another.
• Problems That Arise When Providing Geographic Coordinate Information for Cataloged Maps 11 January 2010 7:50 UTC www.stonybrook.edu [Source type: Reference]

^ Hundreds of different datums have been used to frame position descriptions since the first estimates of the earth's size were made by Aristotle.
• Coordinate Systems Overview 11 January 2010 7:50 UTC www.colorado.edu [Source type: Reference]

^ This overview of coordinate systems for georeferencing provides a brief description of local and global systems for use in precise positioning, navigation, and geographic information systems for the location of points in space.
• Coordinate Systems Overview 11 January 2010 7:50 UTC www.colorado.edu [Source type: Reference]

[1]

## Cartesian coordinates

.Every point that is expressed in spherical coordinates can be expressed as an x y z (Cartesian) coordinate.^ An x,y coordinate defines every point on the plane.
• Auglaize County | GIS Glossary 11 January 2010 7:50 UTC www2.auglaizecounty.org [Source type: Reference]
• GIS GLOSSARY 11 January 2010 7:50 UTC volusia.org [Source type: Reference]

^ If you consider the vector data model, every point has a coordinate; every line's nodes and vertices have coordinates; and every polygon's outlines have coordinates.
• Projections and Coordinate Systems 11 January 2010 7:50 UTC courses.washington.edu [Source type: FILTERED WITH BAYES]

^ The position of one point relative to another can also be shown with the cartesian coordinate system.
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

.This is not a useful method for recording a position on maps but is used to calculate distances and to perform other mathematical operations.^ We then have our model—a paper map—which we can use to perform a calculation.
• Introduction to Spatial Coordinate Systems: Flat Maps for a Round Planet 11 January 2010 7:50 UTC msdn.microsoft.com [Source type: FILTERED WITH BAYES]

^ More methods can be added for other calculations.
• Coordinate and CoordinateList classes - ISO 6709 compliant 11 January 2010 7:50 UTC coordinate.codeplex.com [Source type: FILTERED WITH BAYES]

^ Finally, there is a method to calculate the distance against other coordinate.
• Coordinate and CoordinateList classes - ISO 6709 compliant 11 January 2010 7:50 UTC coordinate.codeplex.com [Source type: FILTERED WITH BAYES]

.The origin is usually the center of the sphere, a point close to the center of the Earth.^ The point of the projection is the center of the sphere.
• GIS Glossary - Geographic Information Science (GIS) 11 January 2010 7:50 UTC www.gisdevelopment.net [Source type: Reference]

^ With NAD 83 the origin of axes was defined to be the center of mass of the Earth as determined from the analysis of the orbits of artificial satellites.
• Standardization of Coordinate Systems and Datums for Data Exchange 11 January 2010 7:50 UTC wvgis.wvu.edu [Source type: Reference]

^ Note that the origin used is the center of the earth as specified in GCC coordinates.
• GeoVRML RFC 1: Coordinate Systems 11 January 2010 7:50 UTC www.ai.sri.com [Source type: Reference]

## Shape of the Earth

.The Earth is not a sphere, but an irregular shape approximating a biaxial ellipsoid.^ To optimize the projection from the geoid into a flat map, the Earth is approximated by an ellipsoid.
• A (not so) short overview of the Geographic Information System GRASS LG #156 11 January 2010 7:50 UTC linuxgazette.net [Source type: FILTERED WITH BAYES]

^ Over time, they have created many different models of the earth's shape including both ellipsoid and spherical forms.
• Geographic and Projected Coordinate Systems - Keys to Creating and Understanding Maps 11 January 2010 7:50 UTC www.fgdl.org [Source type: FILTERED WITH BAYES]

^ The figure that represents the irregular spheroidal shape of the earth is called the geoid.
• GIS Glossary - Geographic Information Science (GIS) 11 January 2010 7:50 UTC www.gisdevelopment.net [Source type: Reference]

.It is nearly spherical, but has an equatorial bulge making the radius at the equator about 0.3% larger than the radius measured through the poles.^ Issac Newton contended that his theory of gravity would mean that the earth would not be perfectly spherical but slightly squashed at the poles and bulging at the equator due to the forces acting upon it as it spins.
• Geoscience Australia: Geodesy - Datums and Coordinates 11 January 2010 7:50 UTC www.ga.gov.au [Source type: Reference]

^ Except near the poles, magnetic longitude will generally be about 70 o greater than geographic longitude.
• Geophysical Coordinate Transformations 11 January 2010 7:50 UTC www-ssc.igpp.ucla.edu [Source type: Academic]

^ To operate over larger regions, we must make use of more than one projection, and therefore more than one map.
• Introduction to Spatial Coordinate Systems: Flat Maps for a Round Planet 11 January 2010 7:50 UTC msdn.microsoft.com [Source type: FILTERED WITH BAYES]

.The shorter axis approximately coincides with axis of rotation.^ The major half axis represents the equatorial radius of the planet, while the minor axis is the polar (and thus the rotational) half axis, which is about 1/298 shorter than the equatorial radius.
• Astronomical Coordinate Systems 11 January 2010 7:50 UTC www.seds.org [Source type: FILTERED WITH BAYES]

.Map-makers choose the true ellipsoid that best fits their need for the area they are mapping.^ In the case of NAD 83 a and f were chosen to give a best fit of the reference ellipsoid to the geoid (mean sea level) for the Earth as a whole.
• Standardization of Coordinate Systems and Datums for Data Exchange 11 January 2010 7:50 UTC wvgis.wvu.edu [Source type: Reference]

^ If a different meridian is specified on an old map, the cataloger records the coordinates in Greenwich, but may choose to give other meridians provided in the notes area of a record (Mangan 2005).
• Problems That Arise When Providing Geographic Coordinate Information for Cataloged Maps 11 January 2010 7:50 UTC www.stonybrook.edu [Source type: Reference]

^ Shape Distance True Direction Area Distortion will vary in at least one of each of the above properties depending on the projection used, as well as the scale of the map, or the spatial extent that is mapped.
• Projections and Coordinate Systems 11 January 2010 7:50 UTC courses.washington.edu [Source type: FILTERED WITH BAYES]

.They then choose the most appropriate mapping of the spherical coordinate system onto that ellipsoid.^ Map projection, coordinate system and map scale ...
• GIS2004 11 January 2010 7:50 UTC www.ees.nmt.edu [Source type: FILTERED WITH BAYES]

^ Projected coordinate systems are referred to as map projections.
• Coordinate systems, map projections, and geographic (datum) transformations 11 January 2010 7:50 UTC edndoc.esri.com [Source type: Reference]

^ Using proven mapping and locating systems technologies, we successfully and accurately map XYZ centerline coordinates and create three-dimensional maps and Geographic Information System (GIS) databases.

.In the United Kingdom there are three common latitude, longitude, height systems in use.^ An example of a coordinate system is latitude and longitude.
• Geographic Information Systems 11 January 2010 7:50 UTC atlas.kennesaw.edu [Source type: Reference]

^ Geographic Coordinate Units -- units of measure used for the latitude and longitude values.
• 4 : Spatial Reference Information — Federal Geographic Data Committee 11 January 2010 7:50 UTC www.fgdc.gov [Source type: Reference]

^ Unit 014 - Latitude and Longitude 1.
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

.The system used by GPS, WGS84, differs at Greenwich from the one used on published maps OSGB36 by approximately 112m.^ Maps for different purposes use different projections.
• Geographic and Projected Coordinate Systems - Keys to Creating and Understanding Maps 11 January 2010 7:50 UTC www.fgdl.org [Source type: FILTERED WITH BAYES]

^ Some geographic coordinate systems provide several transformations into WGS84, which are designed to provide good accuracy in different areas of interest.
• GeographicCoordinateSystem (geotools-gtbuild 2.3.x API) 11 January 2010 7:50 UTC udig.refractions.net [Source type: Reference]

^ Sometimes no transformation exists, or you have to use a third GCS like the World Geodetic System 1984 (WGS84) and combine two transformations.
• Coordinate systems, map projections, and geographic (datum) transformations 11 January 2010 7:50 UTC edndoc.esri.com [Source type: Reference]

.The military system ED50, used by NATO, differs by about 120m to 180m.^ Maps will sometimes either leave out coordinates, or if they do include them, they may provide them using different systems than ones commonly used.
• Problems That Arise When Providing Geographic Coordinate Information for Cataloged Maps 11 January 2010 7:50 UTC www.stonybrook.edu [Source type: Reference]

^ This article includes the parameters required for various coordinate systems, as well as useful information about working with coordinate systems in ArcMap.
• Technical Articles - ESRI Support 11 January 2010 7:50 UTC support.esri.com [Source type: Reference]

^ Each activity aims to capture different aspects of the interdependence between the use of the systems of reference and the navigation in geographical space.
• Remath - Pedagogical Plan 11 January 2010 7:50 UTC remath.itd.cnr.it [Source type: FILTERED WITH BAYES]

[1]
.Though early navigators thought of the sea as a flat surface that could be used as a vertical datum, this is far from reality.^ Some projections use projective geometry, and are drawn on a flat surface with a t-square and a triangle.
• Geographic and Projected Coordinate Systems - Keys to Creating and Understanding Maps 11 January 2010 7:50 UTC www.fgdl.org [Source type: FILTERED WITH BAYES]

^ As before, we could use a globe, but while this may be useful to envision the whole Earth, to achieve the detail needed for most real calculations, a truly gargantuan globe would be required.
• Introduction to Spatial Coordinate Systems: Flat Maps for a Round Planet 11 January 2010 7:50 UTC msdn.microsoft.com [Source type: FILTERED WITH BAYES]

^ Australia's vertical datum is the Australian Height Datum [AHD] which approximates mean sea level and was determined by monitoring tide gauges around the Australian coastline.
• Geoscience Australia: Geodesy - Datums and Coordinates 11 January 2010 7:50 UTC www.ga.gov.au [Source type: Reference]

.The Earth can be thought to have a series of layers of equal potential energy within its gravitational field.^ The first step of approximation is the geoid , which is a theoretical construct defined as a surface of equal gravitational potential.
• Introduction to Spatial Coordinate Systems: Flat Maps for a Round Planet 11 January 2010 7:50 UTC msdn.microsoft.com [Source type: FILTERED WITH BAYES]

^ That is, to take an ordinary VRML model, contained within the children field of the node, and to specify its location on the surface of the earth.
• GeoVRML 1.0 - Nodes 11 January 2010 7:50 UTC www.ai.sri.com [Source type: Reference]

^ If we ignore other forces, a body of water will flow so that its surface has equal gravitational potential.
• Introduction to Spatial Coordinate Systems: Flat Maps for a Round Planet 11 January 2010 7:50 UTC msdn.microsoft.com [Source type: FILTERED WITH BAYES]

.Height is a measurement at right angles to this surface, and although gravity pulls mainly toward the centre of Earth, the geocentre, there are local variations.^ Longitude and latitude are angles measured from the earth's center to a point on the earth's surface.
• Coordinate systems, map projections, and geographic (datum) transformations 11 January 2010 7:50 UTC edndoc.esri.com [Source type: Reference]

^ Latitude and longitude are angles measured from the Earth's center to locations on the Earth's surface.
• Merced County Association of Governments, California, USA 11 January 2010 7:50 UTC www.mcaggis.com [Source type: Reference]

^ The latitude measurement of the Earth is based on 0 to 90 degrees of height (latitude) north and south of the equator.
• Communications device for conveying geographic location information over capacity constrained wireless systems - Patent 7272494 11 January 2010 7:50 UTC www.freepatentsonline.com [Source type: Reference]

.The shape of these layers is irregular but essentially ellipsoidal.^ The most essential tool for navigating around a layer is the Pan tool, the toolbar icon in the shape of a hand.
• Quantum GIS: the Open-Source Geographic Information System 11 January 2010 7:50 UTC www.linuxjournal.com [Source type: FILTERED WITH BAYES]

^ To add to the complexity of these projections of the earth's surface, one must remember that there are mathematical models of the earth's shape - different spheres and ellipsoids - on which these projections can be based.
• Geographic and Projected Coordinate Systems - Keys to Creating and Understanding Maps 11 January 2010 7:50 UTC www.fgdl.org [Source type: FILTERED WITH BAYES]

.The choice of which layer to use for defining height is arbitrary.^ In the case of using the geographical system, the end position of the vector of the displacement is defined by the geographical coordinates lat-long-height.
• Remath - Pedagogical Plan 11 January 2010 7:50 UTC remath.itd.cnr.it [Source type: FILTERED WITH BAYES]

^ Indicates that the attributes which define the masking region ( x , y , width , height ) is established using the bounding box of the element to which the mask is applied.
• Coordinate Systems, Transformations and Units - SVG 1.1 - 20030114 11 January 2010 7:50 UTC www.w3.org [Source type: Reference]

^ Define a height field using geographic coordinates .
• GeoVRML 1.0 - Nodes 11 January 2010 7:50 UTC www.ai.sri.com [Source type: Reference]

.The reference height we have chosen is the one closest to the average height of the world's oceans.^ World Geographic Reference System Index These 15 degree areas are further divided into one degree units identified by 15 characters.
• Coordinate Systems Overview 11 January 2010 7:50 UTC www.colorado.edu [Source type: Reference]

This is called the geoid.[1][5]
.The Earth is not static as points move relative to each other due to continental plate motion, subsidence, and diurnal movement caused by the Moon and the tides.^ The daily east to west motion of celestial objects is caused by the Earths rotation and is known as diurnal motion .

^ Coordinates represent locations on the Earth's surface relative to other locations.
• Auglaize County | GIS Glossary 11 January 2010 7:50 UTC www2.auglaizecounty.org [Source type: Reference]
• GIS GLOSSARY 11 January 2010 7:50 UTC volusia.org [Source type: Reference]

^ In this system, a star or other celestial object moves contrary to Earth's rotation along a circle of constant declination during the course of the day; various effects of this diurnal motion are discussed below .
• Astronomical Coordinate Systems 11 January 2010 7:50 UTC www.seds.org [Source type: FILTERED WITH BAYES]

The daily movement can be as much as a metre. Continental movement can be up to 10 cm a year, or 10 m in a century. A weather system high-pressure area can cause a sinking of 5 mm. Scandinavia is rising by 1 cm a year as a result of the melting of the ice sheets of the last ice age, but neighbouring Scotland is only rising by 0.2 cm. .These changes are insignificant if a local datum is used, but are significant if the global GPS datum is used.^ Patents in all subclasses Using Global Positioning Satellite (GPS or Glonass) .
• System and method for selecting a geographic location to associate with an object - Patent application 11 January 2010 7:50 UTC www.faqs.org [Source type: Reference]

^ In this exercise, you will see how ArcMap applies its default datum transformations and you will learn how to change these settings.
• A new data frame has no coordinate system 11 January 2010 7:50 UTC www.unc.edu [Source type: FILTERED WITH BAYES]

^ GPS tracking – using the Global Positioning System (GPS) to automatically locate the position of a vehicle, person, or animal as it travels over an extended period of time.

[1]

## Expressing latitude and longitude as linear units

.On a spherical surface at sea level, one latitudinal second measures 30.82 metres and one latitudinal minute 1849 metres, and one latitudinal degree is 110.9 kilometres.^ It is measured in degrees, minutes, and seconds from -90 to +90 degrees with 0 being on the celestial equator.

^ Both are measured in degrees, minutes, and seconds.

^ Both coordinates are measured in degrees, minutes, and seconds.

.The circles of longitude, meridians, meet at the geographical poles, with the west-east width of a second being dependent on the latitude.^ The distance east or west of a prime meridian to a point is known as its longitude.
• Orienteering - Geographic Coordinates 11 January 2010 7:50 UTC www.4orienteering.com [Source type: FILTERED WITH BAYES]

^ Every meridian meets every other meridian at the poles.

^ The longitude is the points angular position east or west of the prime meridian.

.On the equator at sea level, one longitudinal second measures 30.92 metres, a longitudinal minute 1855 metres, and a longitudinal degree 111.3 kilometres.^ It is measured in degrees, minutes, and seconds from -90 to +90 degrees with 0 being on the celestial equator.

^ Both coordinates are measured in degrees, minutes, and seconds.

^ Both are measured in degrees, minutes, and seconds.

.At 30° a longitudinal second is 26.76 metres, at Greenwich (51° 28' 38" N) is 19.22 metres, and at 60° it is 15.42 metres.^ To convert 45 33' 22", first multiply 33 minutes by 60, which equals 1,980 seconds.
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

.The width of one longitudinal degree on latitude $\scriptstyle{\phi}\,\!$^ Two additional numeric characters designate the number of minutes of latitude north of the one degree quadrangle boundary latitude.
• Coordinate Systems Overview 11 January 2010 7:50 UTC www.colorado.edu [Source type: Reference]

^ UTM zone numbers designate 6 degree longitudinal strips extending from 80 degrees South latitude to 84 degrees North latitude.
• Coordinate Systems Overview 11 January 2010 7:50 UTC www.colorado.edu [Source type: Reference]

^ At 60 N latitude, one degree of longitude is equal to about 55.52 kilometers (34.5 miles).
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

src="http://images-mediawiki-sites.thefullwiki.org/00/5/2/0/094764007590541.png" /> can be calculated by this formula (to get the width per minute and second, divide by 60 and 3600, respectively):
$\frac{\pi}{180^{\circ}}\cos(\phi)M_r,\,\!$
where Earth's average meridional radius $\scriptstyle{M_r}\,\!$ approximately equals 6,367,449 m. .Due to the average radius value used, this formula is of course not precise.^ For more precise measurements we will use different tools covered later in the course.
• Projections and Coordinate Systems 11 January 2010 7:50 UTC courses.washington.edu [Source type: FILTERED WITH BAYES]

^ In addition, when converting for profiles which place restrictions on precision of real number values, it may be useful to add an additional scaling factor to retain good precision for a specific area.
• Coordinate Systems, Transformations and Units - SVG 1.1 - 20030114 11 January 2010 7:50 UTC www.w3.org [Source type: Reference]
• Coordinate Systems, Transformations and Units – SVG Tiny 1.2 11 January 2010 7:50 UTC dev.w3.org [Source type: Reference]
• Coordinate Systems, Transformations and Units – SVG 1.1 (Second Edition) 11 January 2010 7:50 UTC dev.w3.org [Source type: Reference]
• Coordinate Systems, Transformations and Units 11 January 2010 7:50 UTC dev.w3.org [Source type: Reference]

^ Specifying a value of "none" indicates that a supplemental transformation due to the 'viewBox' attribute must not be used.
• Coordinate Systems, Transformations and Units – SVG Tiny 1.2 11 January 2010 7:50 UTC dev.w3.org [Source type: Reference]

.You can get a better approximation of a longitudinal degree at latitude $\scriptstyle{\phi}\,\!$^ UTM zone numbers designate 6 degree longitudinal strips extending from 80 degrees South latitude to 84 degrees North latitude.
• Coordinate Systems Overview 11 January 2010 7:50 UTC www.colorado.edu [Source type: Reference]

^ These give the location of the cursor, and from the values displayed you can see that these data are latitude and longitude displayed in degrees, minutes and seconds.
• GEO327G/386G  Lab 2 - Map Projections and Coordinate Systems 11 January 2010 7:50 UTC www.geo.utexas.edu [Source type: FILTERED WITH BAYES]
• Geol 2161  Lab 2 - Map Projections and Coordinate Systems 11 January 2010 7:50 UTC cda.morris.umn.edu [Source type: FILTERED WITH BAYES]

src="http://images-mediawiki-sites.thefullwiki.org/00/5/2/0/094764007590541.png" /> by:
$\frac{\pi}{180^{\circ}}\cos(\phi)\sqrt{\frac{a^4\cos(\phi)^2+b^4\sin(\phi)^2}{(a\cos(\phi))^2+(b\sin(\phi))^2}},\,\!$
where .Earth's equatorial and polar radii, $\scriptstyle{a,b}\,\!$^ Denominator of Flattening Ratio -- the denominator of the ratio of the difference between the equatorial and polar radii of the ellipsoid when the numerator is set to 1.
• 4 : Spatial Reference Information — Federal Geographic Data Committee 11 January 2010 7:50 UTC www.fgdc.gov [Source type: Reference]

src="http://images-mediawiki-sites.thefullwiki.org/00/1/8/7/68890881756300538.png" /> equal 6,378,137 m, 6,356,752.3 m, respectively.
Length equivalent at selected latitudes in km
Latitude Town Degree Minute Second ±0.0001°
60° Saint Petersburg 55.65 km 0.927 km 15.42m 5.56m
51° 28' 38" N Greenwich 69.29 km 1.155 km 19.24m 6.93m
45° Bordeaux 78.7 km 1.31 km 21.86m 7.87m
30° New Orleans 96.39 km 1.61 km 26.77m 9.63m
Quito 111.3 km 1.855 km 30.92m 11.13m

## Datums often encountered

.Latitude and longitude values can be based on several different geodetic systems or datums, the most common being WGS 84 used by all GPS equipment.^ It differs from the traditional method of latitude and longitude in several respects.
• A (not so) short overview of the Geographic Information System GRASS LG #156 11 January 2010 7:50 UTC linuxgazette.net [Source type: FILTERED WITH BAYES]

^ Geographic Coordinate Units -- units of measure used for the latitude and longitude values.
• 4 : Spatial Reference Information — Federal Geographic Data Committee 11 January 2010 7:50 UTC www.fgdc.gov [Source type: Reference]

^ Patents in all subclasses Using Global Positioning Satellite (GPS or Glonass) .
• System and method for selecting a geographic location to associate with an object - Patent application 11 January 2010 7:50 UTC www.faqs.org [Source type: Reference]

[6] .Other datums however are significant because they were chosen by a national cartographical organisation as the best method for representing their region, and these are the datums used on printed maps.^ However simple or complex the user's purpose, a GIS is used to access an integrated, geographically referenced database of maps that can be overlaid, combined, and analyzed to user specifications.
• The Basics of Geographic Information Systems 11 January 2010 7:50 UTC www.extension.umn.edu [Source type: Reference]

^ Maps will sometimes either leave out coordinates, or if they do include them, they may provide them using different systems than ones commonly used.
• Problems That Arise When Providing Geographic Coordinate Information for Cataloged Maps 11 January 2010 7:50 UTC www.stonybrook.edu [Source type: Reference]

^ Users can access these information sources using interactive, time-enabled thematic maps.
• By Subject - Maps/Geographic Information Systems - Maps 11 January 2010 7:50 UTC www.lib.washington.edu [Source type: Reference]

.Using the latitude and longitude found on a map may not give the same reference as on a GPS receiver.^ Three pairs of expressions have been derived: each pair is used to calculate the shift in latitude and longitude respectively for .
• Geographic Coordinate System Transformations 11 January 2010 7:50 UTC www.posc.org [Source type: Academic]

^ Georeferencing now usually involves the intersection of one line of latitude and one line of longitude, but as the use of map interfaces increases, more complex georeferencing schemes may appear—such as the use of two lines of latitude and of longitude to form a bounding box or a polygon approximating actual boundaries (Buckland 2007, 381).
• Problems That Arise When Providing Geographic Coordinate Information for Cataloged Maps 11 January 2010 7:50 UTC www.stonybrook.edu [Source type: Reference]

^ Maps will sometimes either leave out coordinates, or if they do include them, they may provide them using different systems than ones commonly used.
• Problems That Arise When Providing Geographic Coordinate Information for Cataloged Maps 11 January 2010 7:50 UTC www.stonybrook.edu [Source type: Reference]

.Coordinates from the mapping system can sometimes be changed into another datum using a simple translation.^ Transformations map coordinates and lengths from a new coordinate system into a previous coordinate system: .
• Coordinate Systems, Transformations and Units – SVG Tiny 1.2 11 January 2010 7:50 UTC www.w3.org [Source type: Reference]
• Coordinate Systems, Transformations and Units – SVG Tiny 1.2 11 January 2010 7:50 UTC dev.w3.org [Source type: Reference]
• Coordinate Systems, Transformations and Units – SVG 1.1 (Second Edition) 11 January 2010 7:50 UTC dev.w3.org [Source type: Reference]
• Coordinate Systems, Transformations and Units 11 January 2010 7:50 UTC dev.w3.org [Source type: Reference]

^ Transformations map coordinates and lengths from a new coordinate system into a previous coordinate system:        .
• Coordinate Systems, Transformations and Units - SVG 1.1 - 20030114 11 January 2010 7:50 UTC www.w3.org [Source type: Reference]

^ What geographic coordinate system or datum should be used for my data?
• Technical Articles - ESRI Support 11 January 2010 7:50 UTC support.esri.com [Source type: Reference]

For example, to convert from ETRF89 (GPS) to the Irish Grid add 49 metres to the east, and subtract 23.4 metres from the north.[7] .More generally one datum is changed into any other datum using a process called Helmert transformations.^ Their uses include comparing positions, calculating distances, and general assistance in navigating from one point or place to another.
• Problems That Arise When Providing Geographic Coordinate Information for Cataloged Maps 11 January 2010 7:50 UTC www.stonybrook.edu [Source type: Reference]

^ GIS is used in digital cartography modeling as a (semi)automated process of making maps, so called Automated Cartography.
• Geographic information system - Wiki.gis.com 11 January 2010 7:50 UTC wiki.gis.com [Source type: Reference]

^ Transformation: The process that converts coordinates from one coordinate system to another through translation, rotation, and scaling.

.This involves converting the spherical coordinates into Cartesian coordinates and applying a seven parameter transformation (translation, three-dimensional rotation), and converting back.^ Coordinate: An x,y location in a Cartesian coordinate system or an x,y,z coordinate in a three dimensional system.

^ The simplest transformation to implement involves applying shifts to the three geocentric coordinates.
• Geographic Coordinate System Transformations 11 January 2010 7:50 UTC www.posc.org [Source type: Academic]

^ The transformations may be most readily achieved by first expressing the observed or source geographical coordinates in terms of three dimensional XYZ cartesian values (geocentric coordinates) instead of the normal angular expressions of latitude and longitude.
• Geographic Coordinate System Transformations 11 January 2010 7:50 UTC www.posc.org [Source type: Academic]

[1]
In popular GIS software, data projected in latitude/longitude is often represented as a 'Geographic Coordinate System'. For example, data in latitude/longitude if the datum is the North American Datum of 1983 is denoted by 'GCS North American 1983'.

## Geostationary coordinates

.Geostationary satellites (e.g., television satellites) are over the equator at a specific point on Earth, so their position related to Earth is expressed in longitude degrees only.^ In the image below, the specific point on the surface of the earth is specified by the coordinate (60 °.
• Projections and Coordinate Systems 11 January 2010 7:50 UTC courses.washington.edu [Source type: FILTERED WITH BAYES]

^ Per the original definition, the Earth was divided into zones 6 degrees wide along the equator, starting at 180 deg.

^ Geographic -- the quantities of latitude and longitude which define the position of a point on the Earth's surface with respect to a reference spheroid.
• 4 : Spatial Reference Information — Federal Geographic Data Committee 11 January 2010 7:50 UTC www.fgdc.gov [Source type: Reference]

Their latitude is always zero, that is, over the equator.

## Notes

1. ^ a b c d e f A Guide to coordinate systems in Great Britain v1.7 Oct 2007 D00659 accessed 14.4.2008
2. ^ http://wwp.millennium-dome.com/info/conference.htm
3. ^ The French Institut Géographique National (IGN) still displays a latitude and longitude on its maps centred on a meridian that passes through Paris
4. ^ Haswell, Charles Haynes (1920). Mechanics' and Engineers' Pocket-book of Tables, Rules, and Formulas. Harper & Brothers. Retrieved 2007-04-09.
5. ^ DMA Technical Report Geodesy for the Layman, The Defense Mapping Agency, 1983
6. ^ WGS 84 is the default datum used in most GPS equipment, but other datums can be selected.
7. ^ Making maps compatible with GPS Government of Ireland 1999. Accessed 15.4.2008

## References

• Portions of this article are from Jason Harris' "Astroinfo" which is distributed with KStars, a desktop planetarium for Linux/KDE. See [1]

# Genealogy

Up to date as of February 01, 2010

### From Familypedia

For the use of coordinates on Wikipedia pages see: Wikipedia:WikiProject Geographical coordinates
Map of Earth showing lines of latitude (horizontally) and longitude (vertically), Eckert VI projection; 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.^ Must be null for a geographic or non-Earth coordinate system.
• Coordinate Systems (Spatial Reference Systems) 11 January 2010 7:50 UTC download.oracle.com [Source type: Reference]

^ So any where on Earth can be located by specifying its geographic coordinates in latitude and longitude.

^ Geographic coordinate system .

## First and second dimensions: latitude and longitude

Latitude phi (φ) and Longitude lambda (λ)
.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 (Borrowing from theories of the ancient Babylonians' angle) (360°).^ Earth, as a circle, is divided into 360 degrees (360 o ).
• HAMMOND WAC - Latitude and Longitude 25 September 2009 5:27 UTC www.hammondmap.com [Source type: General]

^ Each circle is divided into 360 degrees, each degree into 60 minutes, and each minute into 60 seconds.
• Use of Geographic Coordinates to Pinpoint Location in Map Reading 11 January 2010 7:50 UTC www.map-reading.com [Source type: FILTERED WITH BAYES]
• Orienteering - Geographic Coordinates 11 January 2010 7:50 UTC www.4orienteering.com [Source type: FILTERED WITH BAYES]

^ Midway between the poles, the equator, a great circle (that is, a circle whose centre is also the centre of the Earth), divides the Earth into northern and southern hemispheres .
• Latitude and Longitude - ninemsn Encarta 25 September 2009 5:27 UTC au.encarta.msn.com [Source type: FILTERED WITH BAYES]

• 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.^ The latitude lines are concentric circles that become smaller near the poles.
• SpatialV1.2 - Geographic coordinate system 11 January 2010 7:50 UTC publib.boulder.ibm.com [Source type: Reference]

^ Thus, lines of latitude are also called parallels .
• HAMMOND WAC - Latitude and Longitude 25 September 2009 5:27 UTC www.hammondmap.com [Source type: General]

^ Because these circles are parallel to the Equator, they are called parallels of latitude.

.Each pole is 90 degrees: the north pole 90° N; the south pole 90° S. The 0° parallel of latitude is designated the equator, an imaginary line that divides the globe into the Northern and Southern Hemispheres.
• longitude (abbreviation: Long.^ The equator is designated as having a Northing value of 0 for northern hemisphere coordinates.
• The GIS Primer - Nature of Geographic Information 11 January 2010 7:50 UTC www.innovativegis.com [Source type: Reference]

^ Under this system, Kentucky is divided into the North and South Zones.
• Kentucky GIAC Kentucky State Plane Coordinate System 11 January 2010 7:50 UTC gis.ky.gov [Source type: Reference]
• Kentucky State Plane Coordinate Systems 11 January 2010 7:50 UTC ngs.ky.gov [Source type: Reference]

^ Meridians: north-south lines connecting the poles.
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

) 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.^ The line of zero longitude is called the prime meridian.
• Coordinate systems, map projections, and geographic (datum) transformations 11 January 2010 7:50 UTC edndoc.esri.com [Source type: Reference]

^ The curves with the same longitude are called "the meridians".
• Global Distances 22 September 2009 20:29 UTC www.shokhirev.com [Source type: FILTERED WITH BAYES]

^ Lines of similar longitude are half-circles called meridians.
• Costa Rica GPS Wiki | GPS / Coordinate Systems 11 January 2010 7:50 UTC www.words2u.net [Source type: Reference]

.All meridians are halves of great circles, and are not parallel: by definition they converge at the north and south poles.^ Half circles from pole to pole, which are all perpendicular to the equatorialplane, are called meridians .
• Astronomical Coordinate Systems 11 January 2010 7:50 UTC www.seds.org [Source type: FILTERED WITH BAYES]

^ Meridians: north-south lines connecting the poles.
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

^ The Longitude is meaningless at the north pole (and the south pole too).

.The line passing through the (former) Royal Observatory (near London in the UK) is the international zero-longitude reference line, the Prime Meridian.^ Equator and Prime Meridian The Equator and the Prime Meridian are the reference lines used to measure latitude and longitude.
• Cynthia Lanius' Lessons: Mathematics of Cartography:Map Coordinate System 11 January 2010 7:50 UTC math.rice.edu [Source type: Reference]

^ Passes through the old Royal Observatory in Greenwich, England.
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

^ The prime meridian is established by international agreement and currently runs through the Royal Observatory in Greenwich, England.
• Cartography - Latitude And Longitude 25 September 2009 5:27 UTC science.jrank.org [Source type: Reference]

The antipodal meridian of Greenwich is both 180°W and 180°E.
.By combining these two angles, the horizontal position of any location on Earth can be specified.^ By combining these two angles, any location on Earth can be specified.
• Geographic Coordinates 11 January 2010 7:50 UTC docs.kde.org [Source type: FILTERED WITH BAYES]

^ The schema described can be applied to the combination of horizontal position with a third non-spatial parameter which varies monotonically with height or depth.
• ISO 19111:2007 - Geographic information -- Spatial referencing by coordinates 11 January 2010 7:50 UTC www.iso.org [Source type: Reference]

^ The GCDB is designed to be the base layer which anchors the resource data to the legal description of the land and its position or location on the earth’s surface.
• Geographic Coordinate Database (GCDB) 22 September 2009 20:29 UTC www.blm.gov [Source type: Reference]

.For example, Baltimore (in the USA) has a latitude of 39.3° North, and a longitude of 76.6° West (39.3° N 76.6° W).^ Lines of latitude run east-west but north-south distances are measured between them.
• Use of Geographic Coordinates to Pinpoint Location in Map Reading 11 January 2010 7:50 UTC www.map-reading.com [Source type: FILTERED WITH BAYES]
• Orienteering - Geographic Coordinates 11 January 2010 7:50 UTC www.4orienteering.com [Source type: FILTERED WITH BAYES]
• SurvivalIQ Handbook: Land Navigation - Grids - Geographic coordinates 11 January 2010 7:50 UTC www.survivaliq.com [Source type: Reference]

^ The Equirectangular coordinate system is essentially a direct scaling of longitudes and latitudes to distances east and north, with the scaling selected such that distortion is minimized along the central latitude parallel.
• NMPlot User's Guide, Chapter 20: Geographic Coordinate Systems 11 January 2010 7:50 UTC www.wasmerconsulting.com [Source type: Reference]

^ A prime meridian is defined by the position of some prominent feature; positive longitude is in the direction of rotation, and positive latitude is in the direction of the north pole.

.So, a vector drawn from the center of the earth to a point 39.3° north of the equator and 76.6° west of Greenwich will pass through Baltimore.^ So, a vector drawn from the center of the Earth to a point 39.3 degrees above the Equator and 76.6 degrees west of Greenwich, England will pass through Baltimore.
• Geographic Coordinates 11 January 2010 7:50 UTC kstars.sourceforge.net [Source type: FILTERED WITH BAYES]
• Geographic Coordinates 11 January 2010 7:50 UTC docs.kde.org [Source type: FILTERED WITH BAYES]

^ The geodetic longitude of a point is the angle between a reference plane and a plane passing through the point, both planes being perpendicular to the equatorial plane.
• Coordinate Systems Overview 11 January 2010 7:50 UTC www.colorado.edu [Source type: Reference]

^ The International Meridian Conference of 1884 adopted the Prime Meridian line passing through the Greenwich Observatory near London, England.
• Cynthia Lanius' Lessons: Mathematics of Cartography:Map Coordinate System 11 January 2010 7:50 UTC math.rice.edu [Source type: Reference]

.This latitude/longitude "webbing" is known as the common graticule.^ It is known as the latitude and longitude grid .
• HAMMOND WAC - Latitude and Longitude 25 September 2009 5:27 UTC www.hammondmap.com [Source type: General]

^ These are data with known latitude, longitude, and elevation, or other horizontal and vertical coordinates.
• Down to Earth: Geographical Information for Sustainable Development in Africa 11 January 2010 7:50 UTC www.nap.edu [Source type: Academic]
• Down to Earth: Geographical Information for Sustainable Development in Africa 11 January 2010 7:50 UTC www.nap.edu [Source type: Academic]

^ Right-click (CTRL-click) a known location (on for which you know the actual latitude and longitude) in the map's background image and choose Add benchmark...

.There is also a complementary transverse graticule (meaning the graticule is shifted 90°, so that the poles are on the horizontal equator), upon which all spherical trigonometry is ultimately based.^ There are 90 degrees from the equator to each pole, and sixty minutes in each degree.
• Cartography - Latitude And Longitude 25 September 2009 5:27 UTC science.jrank.org [Source type: Reference]

^ Latitude runs from 0° at the equator to 90°N or 90°S at the poles.
• GeoSystems: Latitude and Longitude 25 September 2009 5:27 UTC www-personal.umich.edu [Source type: Reference]

^ Parallels are numbered from 0° at the Equator to 90° at the poles.
• What is Terrestrial coordinate system? - A definition of Terrestrial coordinate system from the ecomii science encyclopedia 11 January 2010 7:50 UTC www.ecomii.com [Source type: FILTERED WITH BAYES]

.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").^ These are usually referred by degrees, minutes, and seconds.
• * Geographic - (GIS): Definition 11 January 2010 7:50 UTC en.mimi.hu [Source type: Academic]
• The GIS Primer - Nature of Geographic Information 11 January 2010 7:50 UTC www.innovativegis.com [Source type: Reference]

^ Latitude coordinates are also cascaded to the full degree (i.e., first two digits): N451430 is North, 45 degrees, 14 minutes, 30 seconds; it is also cascaded to N45.
• File 89, GeoRef: Geographic Coordinates Fields 11 January 2010 7:50 UTC support.dialog.com [Source type: Reference]

^ Latitude and longitude values are traditionally measured either in decimal degrees or in degrees, minutes, and seconds (DMS).
• Coordinate systems, map projections, and geographic (datum) transformations 11 January 2010 7:50 UTC edndoc.esri.com [Source type: Reference]

There are several formats for degrees, all of them appearing in the same Lat-Long order:
• DMS Degree:Minute:Second (49°30'00"-123d30m00s)
• DM Degree:Minute (49°30.0'-123d30.0m)
• DD Decimal Degree (49.5000°-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.^ This is an introductory course in geographic information systems.
• Geographic Information Systems AWER 4930 11 January 2010 7:50 UTC www.gis.usu.edu [Source type: FILTERED WITH BAYES]

^ Degrees, Minutes, Seconds - 950'24.10" Degrees, Minutes, Decimal Minutes - 950.4017 Degree, Decimal Degrees - 9.8403 To convert seconds to decimal minutes, divide the seconds by 60.
• Costa Rica GPS Wiki | GPS / Coordinate Systems 11 January 2010 7:50 UTC www.words2u.net [Source type: Reference]

^ Here the first number is degrees, the second is minutes, denoted ', and the third is seconds, denoted ''.
• Costa Rica GPS Wiki | GPS / Coordinate Systems 11 January 2010 7:50 UTC www.words2u.net [Source type: Reference]

.On a spherical surface at sea level, one latitudinal second measures 30.82 metres and one latitudinal minute 1849 metres.^ Both are measured in degrees, minutes, and seconds.

^ The ellipsoidal height of a location is defined as the elevation of the location above the geoid (essentially a modeled surface representing mean sea level) and the separation of the geoid surface from the ellipsoidal surface.

^ Minutes and whole seconds must be padded with a single leading zero if they are only one digit long.
• WORLD DISTANCE CALCULATOR GEOGRAPHIC COORDINATES AND AZIMUTH 22 September 2009 20:29 UTC www.infoairports.com [Source type: FILTERED WITH BAYES]

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.^ First column is the longitude, second column latitude.
• Download Geographic to UTM coordinates - Geographic to UTM coordinates - Complete and easy to use GUI for converting Geographic to UTM coordinates. - Softpedia 22 September 2009 20:29 UTC webscripts.softpedia.com [Source type: General]

^ Longitude indicates the number of degrees east or west of the prime meridian (0 degrees).
• File 89, GeoRef: Geographic Coordinates Fields 11 January 2010 7:50 UTC support.dialog.com [Source type: Reference]

^ Longitude is the location east or west on the map.
• Costa Rica GPS Wiki | GPS / Coordinate Systems 11 January 2010 7:50 UTC www.words2u.net [Source type: Reference]

.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 (51° 28' 38" N) and 15.42 metres on the 60th parallel.^ The ellipsoidal height of a location is defined as the elevation of the location above the geoid (essentially a modeled surface representing mean sea level) and the separation of the geoid surface from the ellipsoidal surface.

^ The best of these models can represent the shape of the earth over the smoothed, averaged sea-surface to within about one-hundred meters.
• Coordinate Systems Overview 11 January 2010 7:50 UTC www.colorado.edu [Source type: Reference]

^ This unit provides an overview of latitude and longitude, including: Earth rotation, the North and South Poles, and the Equator Parallels of latitude and meridians of longitude Determination of north or south position with latitude The use of longitude to determine east or west position The measurement of latitude and longitude with degrees, minutes, and seconds Learning Outcomes .
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

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.^ One degree of latitude is, on average, about equal to 60 miles, but varies because the earth is not perfectly spherical.

^ Parallel —A circle or approximation of a circle on the surface of the Earth, parallel to the Equator and connecting points of equal latitude.
• Latitude and Longitude 25 September 2009 5:27 UTC www-atlas.usgs.gov [Source type: Reference]

.Due to the average radius value used, this formula is of course not precise due to Earth's flattening.^ The calculations use a unit radius (radius = 1) for the earth.
• Geographic Midpoint Calculation Methods 11 January 2010 7:50 UTC www.geomidpoint.com [Source type: General]

^ The radius often used when modelling the earth as a sphere is 6371 000 meters.
• Geoscience Australia: Geodesy - Datums and Coordinates 11 January 2010 7:50 UTC www.ga.gov.au [Source type: Reference]

^ PRECISION NOTE: WGRS coordinates are only accurate to within 0.75 meters, due to the rigid formatting of the strings and the precision used by the format.

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.^ Because the earth is not a perfect sphere, the equatorial circumfererence does not equal that of the meridians.
• Unit 014 - Latitude and Longitude 25 September 2009 5:27 UTC www.ncgia.ucsb.edu [Source type: Reference]

^ B is numerically equal to the field at the equator on the surface of the Earth if distances are measured in Earth radii.
• Geophysical Coordinate Transformations 11 January 2010 7:50 UTC www-ssc.igpp.ucla.edu [Source type: Academic]

^ Type: real Domain: Semi-major Axis > 0.0 Denominator of Flattening Ratio -- 4.1.4.4 the denominator of the ratio of the difference between the equatorial and polar radii of the ellipsoid when the numerator is set to 1.
• Spatial Reference info: FGDC metadata content standard 11 January 2010 7:50 UTC geology.usgs.gov [Source type: Reference]

.The equator is the fundamental plane of all geographic coordinate systems.^ Geographic coordinate system .

^ The projected or geographic coordinate system code.
• Entity R_COORDINATE_REF_SYSTEM in Schema Seabed 11 January 2010 7:50 UTC www.ocean.slb.com [Source type: Reference]
• Entity COORDINATE_SYSTEM in Schema Seabed 11 January 2010 7:50 UTC www.ocean.slb.com [Source type: Reference]

^ In the ecliptical coordinate system , the fundamental reference plane is chosen to be the ecliptic , i.e.
• Astronomical Coordinate Systems 11 January 2010 7:50 UTC www.seds.org [Source type: FILTERED WITH BAYES]

.All spherical coordinate systems define such a fundamental plane.^ This system is a spherical coordinate system.
• Coordinate Systems, Datums, and Map Projections 11 January 2010 7:50 UTC geosun.sjsu.edu [Source type: Reference]

^ The coordinate system that the Spatial_Correlation is defined in.
• Entity COORDINATE_SYSTEM in Schema Seabed 11 January 2010 7:50 UTC www.ocean.slb.com [Source type: Reference]

^ In the ecliptical coordinate system , the fundamental reference plane is chosen to be the ecliptic , i.e.
• Astronomical Coordinate Systems 11 January 2010 7:50 UTC www.seds.org [Source type: FILTERED WITH BAYES]

.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.^ Intermediate coordinates are used to specify a range of values for latitude and a range for longitude.
• File 89, GeoRef: Geographic Coordinates Fields 11 January 2010 7:50 UTC support.dialog.com [Source type: Reference]

^ When should latitude and longitude values be negative?
• Questions about Latitude and Longitude - Ask.com 25 September 2009 5:27 UTC www.ask.com [Source type: General]

^ Latitude, Longitude, Height The most commonly used coordinate system today is the latitude, longitude, and height system.
• Coordinate Systems Overview 11 January 2010 7:50 UTC www.colorado.edu [Source type: Reference]

.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.^ A location on the Earth's surface will have different coordinates for different datums.
• Map Projections and Coordinate Systems: Part 2 11 January 2010 7:50 UTC www.geowebguru.com [Source type: FILTERED WITH BAYES]

^ The latitude and longitude are located on maps of the earth.
• Questions about Latitude and Longitude - Ask.com 25 September 2009 5:27 UTC www.ask.com [Source type: General]

^ The latitude and longitude of a projection point are the same as those of the associated surface reference station.
• Standardization of Coordinate Systems and Datums for Data Exchange 11 January 2010 7:50 UTC wvgis.wvu.edu [Source type: Reference]

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.^ Each position is described by a set of coordinates based on a specified coordinate reference system.

^ Coordinates represent locations on the Earth's surface relative to other locations.
• Auglaize County | GIS Glossary 11 January 2010 7:50 UTC www2.auglaizecounty.org [Source type: Reference]
• GIS GLOSSARY 11 January 2010 7:50 UTC volusia.org [Source type: Reference]
• WebGIS.net :: Glossary 11 January 2010 7:50 UTC www.webgis.net [Source type: Reference]

^ This paper specifies XML encoding of data defining some coordinate reference systems.

.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).^ Elsewhere, the surface of the Earth may rise (or fall) above (or below) the geoid.
• Introduction to Spatial Coordinate Systems: Flat Maps for a Round Planet 11 January 2010 7:50 UTC msdn.microsoft.com [Source type: FILTERED WITH BAYES]

^ In physics, the level of mean sea level is a surface of gravitational equipotential or geoid .
• Map Projections and Coordinate Systems: Part 2 11 January 2010 7:50 UTC www.geowebguru.com [Source type: FILTERED WITH BAYES]

^ Coordinate System A reference system for defining precise locations on the Earth's surface.
• 07a Geographic Reference Systems 11 January 2010 7:50 UTC www.microimages.com [Source type: Reference]

.The distance to the earth's center can be used both for very deep positions and for positions in space.^ Their uses include comparing positions, calculating distances, and general assistance in navigating from one point or place to another.
• Problems That Arise When Providing Geographic Coordinate Information for Cataloged Maps 11 January 2010 7:50 UTC www.stonybrook.edu [Source type: Reference]

^ Sometimes "false easting" and "false northings" are used so that all X's increase as you go eastward, and all Y's increase as you go northward, and both X's and Y's may be adjusted to be positive numbers.

^ Note that the origin used is the center of the earth as specified in GCC coordinates.
• GeoVRML RFC 1: Coordinate Systems 11 January 2010 7:50 UTC www.ai.sri.com [Source type: Reference]

.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.^ Height of Perspective Point Above Surface -- height of viewpoint above the Earth, expressed in meters.
• 4 : Spatial Reference Information — Federal Geographic Data Committee 11 January 2010 7:50 UTC www.fgdc.gov [Source type: Reference]

^ Q10330 -  I need to project some unprojected point coordinates to a coordinate system in order to use the point data in distance calculations.
• TatukGIS FAQ - DK - Geographic Coordinate Systems, Reprojecting... 11 January 2010 7:50 UTC www.tatukgis.com [Source type: Reference]

^ See Also : angular unit , datum , prime meridian [ coordinate system s] A reference system that uses latitude and longitude to define the location s of points on the surface of a sphere or spheroid .
• * Geographic - (GIS): Definition 11 January 2010 7:50 UTC en.mimi.hu [Source type: Academic]

## Geostationary coordinates

Geostationary satellites (e.g., television satellites ) are over the equator. .So, their position related to Earth is expressed in longitude degrees.^ Longitude and latitude are coordinates that relate to the feature's positions on the spherical earth.
• Geoscience Australia: Geodesy - Datums and Coordinates 11 January 2010 7:50 UTC www.ga.gov.au [Source type: Reference]

^ Geographic position is related to the shape of the Earth.
• Unit 012 - Position on the Earth 11 January 2010 7:50 UTC www.ncgia.ucsb.edu [Source type: Reference]

^ Earth and the meridian of Greenwich (UK) which is the international zero-longitude point (longitude=0 degrees).
• Remath - Pedagogical Plan 11 January 2010 7:50 UTC remath.itd.cnr.it [Source type: FILTERED WITH BAYES]

.Their latitude does not change, and is always zero over the equator.^ The absolute value of the geocentric latitude is always smaller or equal (at poles and equator) to the absolute value of the geographical latitude.
• Astronomical Coordinate Systems 11 January 2010 7:50 UTC www.seds.org [Source type: FILTERED WITH BAYES]

^ Latitude can have the same numerical value north or south of the equator, so the direction N or S must always be given.
• Use of Geographic Coordinates to Pinpoint Location in Map Reading 11 January 2010 7:50 UTC www.map-reading.com [Source type: FILTERED WITH BAYES]
• Orienteering - Geographic Coordinates 11 January 2010 7:50 UTC www.4orienteering.com [Source type: FILTERED WITH BAYES]
• SurvivalIQ Handbook: Land Navigation - Grids - Geographic coordinates 11 January 2010 7:50 UTC www.survivaliq.com [Source type: Reference]

## References

• Portions of this article are from Jason Harris' "Astroinfo" which is distributed with KStars, a desktop planetarium for Linux/KDE. See [1]

# Simple English

[[File:|thumb|440px|Map of Earth showing lines of latitude (horizontally) and longitude (vertically), Eckert VI projection; large version (pdf, 1.8MB)[dead link]]] A Geographical Coordinate System is a Coordinate system. This means that every place can be specified by a set of three numbers, called coordinates.

A full circle can be divided into 360 degrees (or 360°); this was first done by the Babylonians; Ancient Greeks, like Ptolemy later extended the theory.

Today, degrees are divided further. There are minutes, and seconds; 1 minute (or 1') in this context is 1/60 of a degree; 1 second (or 1") is 1/60 of a minute.

The first concept needed is called latitude (Lat, or the Greek symbol "phi", $\scriptstyle\left\{\phi\right\}\,\!$). For it, the Earth is cut up into 180 circles, from the Equator. The poles are at 90°, the North Pole is at 90° N(orth), the South Pole is at 90° S(outh). Places with the same latitude are on a circle, around the Earth.

The other concept is called longitude (Long, or the Greek symbol "lambda", $\scriptstyle\left\{\lambda\right\}\,\!$), sometimes referred to as "meridian". The 0° longitude line (or zero meridian) goes through the Royal Observatory in Greenwich. Greenwich is a part of London. Then lines are drawn in a similar way; the opposite (or "antipodal") meridian of Greenwich is considered both 180°W(est), and 180°E(ast).

The third number is the height, altitude, or depth. This is given with respect to some fixed (usually easily calculable point). One of these is called Mean Sea Level.

# Citable sentences

Up to date as of November 30, 2010

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