World Geodetic System The World Geodetic System ( WGS ) is a standard for use in cartography , geodesy , and navigation . It comprises a standard coordinate frame for the Earth , a standard spheroid al reference surface ( the " datum " or " reference ellipsoid " ) for raw altitude data , and a gravitation al equipotential surface ( the " geoid " ) that defines the " nominal sea level " . The latest revision is WGS 84 ( aka WGS 1984 , EPSG : 4326 ) , established in 1984 and last revised in 2004 . Earlier schemes included WGS 72 , WGS 66 , and WGS 60 . WGS 84 is the reference coordinate system used by the Global Positioning System . Main parameters . The coordinate origin of WGS 84 is meant to be located at the Earth ' s center of mass ; the error is believed to be less than 2 cm . The WGS 84 meridian of zero longitude is the IERS Reference Meridian , 5 . 31 arc seconds or east of the Greenwich meridian at the latitude of the Royal Observatory . The WGS 84 datum surface is an oblate spheroid ( ellipsoid ) with major ( equatorial ) radius " a " = m at the equator and flattening " f " = 1 / . The polar semi - minor axis " b " then equals " a " times ( 1− " f " ) , or m . Presently WGS 84 uses the EGM96 ( Earth Gravitational Model 1996 ) geoid , revised in 2004 . This geoid defines the nominal sea level surface by means of a spherical harmonics series of degree 360 ( which provides about 100 km horizontal resolution ) . The deviations of the EGM96 geoid from the WGS 84 reference ellipsoid range from about −105 m to about + 85 m . EGM96 differs from the original WGS 84 geoid , referred to as EGM84 . History . Efforts to supplement the various national surveying systems began in the 19th century with F . R . Helmert ' s famous books ( " Mathematical and Physical Theory of Physical Geodesy " ) . Austria and Germany founded the " Zentralbüro für die Internationale Erdmessung " ( Central Bureau of International Geodesy ) , and a series of global ellipsoid s of the Earth were derived ( e . g . , Helmert 1906 , Hayford 1910 / 1924 ) . A unified geodetic system for the whole world became essential in the 1950s for several reasons : In the late 1950s , the United States Department of Defense , together with scientists of other institutions and countries , began to develop the needed world system to which geodetic data could be referred and compatibility established between the coordinates of widely separated sites of interest . Efforts of the U . S . Army , Navy and Air Force were combined leading to the DoD World Geodetic System 1960 ( WGS 60 ) . The term " datum " as used here refers to a smooth surface somewhat arbitrarily defined as zero elevation , consistent with a set of surveyor ' s measures of distances between various stations , and differences in elevation , all reduced to a grid of latitudes , longitudes , and elevations . Heritage surveying methods found elevation differences from a local horizontal determined by the spirit level , plumb line , or an equivalent device that depends on the local gravity field ( see physical geodesy ) . As a result , the elevations in the data are referenced to the geoid , a surface that is not readily found using satellite geodesy . The latter observational method is more suitable for global mapping . Therefore , a motivation , and a substantial problem in the WGS and similar work is to patch together data that were not only made separately , for different regions , but to re - reference the elevations to an ellipsoid model rather than to the geoid . In accomplishing WGS 60 , a combination of available surface gravity data , astro - geodetic data and results from HIRAN and Canadian SHORAN surveys were used to define a best - fitting ellipsoid and an earth - centered orientation for each of initially selected datum . ( Every datum is relatively oriented with respect to different portions of the geoid by the astro - geodetic methods already described . ) The sole contribution of satellite data to the development of WGS 60 was a value for the ellipsoid flattening which was obtained from the nodal motion of a satellite . Prior to WGS 60 , the U . S . Army and U . S . Air Force had each developed a world system by using different approaches to the gravimetric datum orientation method . To determine their gravimetric orientation parameters , the Air Force used the mean of the differences between the gravimetric and astro - geodetic deflections and geoid heights ( undulations ) at specifically selected stations in the areas of the major datums . The Army performed an adjustment to minimize the difference between astro - geodetic and gravimetric geoid s . By matching the relative astro - geodetic geoids of the selected datums with an earth - centered gravimetric geoid , the selected datums were reduced to an earth - centered orientation . Since the Army and Air Force systems agreed remarkably well for the NAD , ED and TD areas , they were consolidated and became WGS 60 . The United States Department of Defense World Geodetic System 1966 . Steps to the improvement of a global system were the Astrogeoid of Irene Fischer and the astronautic Mercury datum . In January 1966 , a World Geodetic System Committee composed of representatives from the United States Army , Navy and Air Force , was charged with the responsibility of developing an improved WGS needed to satisfy mapping , charting and geodetic requirements . Additional surface gravity observations , results from the extension of triangulation and trilateration networks , and large amounts of Doppler and optical satellite data had become available since the development of WGS 60 . Using the additional data and improved techniques , WGS 66 was produced which served DoD needs for about five years after its implementation in 1967 . The defining parameters of the WGS 66 Ellipsoid were the flattening ( 1 / 298 . 25 ) , determined from satellite data and the semimajor axis ( 6 , 378 , 145 meters ) , determined from a combination of Doppler satellite and astro - geodetic data . A worldwide 5° × 5° mean free air gravity anomaly field provided the basic data for producing the WGS 66 gravimetric geoid . Also , a geoid referenced to the WGS 66 Ellipsoid was derived from available astrogeodetic data to provide a detailed representation of limited land areas . The United States Department of Defense World Geodetic System 1972 . After an extensive effort extending over a period of approximately three years , the Department of Defense World Geodetic System 1972 was completed . Selected satellite , surface gravity and astrogeodetic data available through 1972 from both DoD and non - DoD sources were used in a Unified WGS Solution ( a large scale least squares adjustment ) . The results of the adjustment consisted of corrections to initial station coordinates and coefficients of the gravitational field . The largest collection of data ever used for WGS purposes was assembled , processed and applied in the development of WGS 72 . Both optical and electronic satellite data were used . The electronic satellite data consisted , in part , of Doppler data provided by the U . S . Navy and cooperating non - DoD satellite tracking stations established in support of the Navy ' s Navigational Satellite System ( NNSS ) . Doppler data was also available from the numerous sites established by GEOCEIVERS during 1971 and 1972 . Doppler data was the primary data source for WGS 72 ( Figure 38 ) . Additional electronic satellite data was provided by the SECOR ( Sequential Collation of Range ) Equatorial Network completed by the U . S . Army in 1970 . Optical satellite data from the Worldwide Geometric Satellite Triangulation Program was provided by the BC - 4 camera system ( Figure 39 ) . Data from the Smithsonian Astrophysical Observatory was also used which included camera ( Baker Nunn ) and some laser ranging . The surface gravity field used in the Unified WGS Solution consisted of a set of 410 10° × 10° equal area mean free air gravity anomalies determined solely from terrestrial data . This gravity field includes mean anomaly values compiled directly from observed gravity data wherever the latter was available in sufficient quantity . The value for areas of sparse or no observational data were developed from geophysically compatible gravity approximations using gravity - geophysical correlation techniques . Approximately 45 percent of the 410 mean free air gravity anomaly values were determined directly from observed gravity data . The astrogeodetic data in its basic form consists of deflection of the vertical components referred to the various national geodetic datums . These deflection values were integrated into astrogeodetic geoid charts referred to these national datums . The geoid heights contributed to the Unified WGS Solution by providing additional and more detailed data for land areas . Conventional ground survey data was included in the solution to enforce a consistent adjustment of the coordinates of neighboring observation sites of the BC - 4 , SECOR , Doppler and Baker - Nunn systems . Also , eight geodimeter long line precise traverses were included for the purpose of controlling the scale of the solution . The Unified WGS Solution , as stated above , was a solution for geodetic positions and associated parameters of the gravitational field based on an optimum combination of available data . The WGS 72 ellipsoid parameters , datum shifts and other associated constants were derived separately . For the unified solution , a normal equation matrix was formed based on each of the mentioned data sets . Then , the individual normal equation matrices were combined and the resultant matrix solved to obtain the positions and the parameters . The value for the semimajor axis ( a ) of the WGS 72 Ellipsoid is 6 378 135 meters . The adoption of an a - value 10 meters smaller than that for the WGS 66 Ellipsoid was based on several calculations and indicators including a combination of satellite and surface gravity data for position and gravitational field determinations . Sets of satellite derived station coordinates and gravimetric deflection of the vertical and geoid height data were used to determine local - to - geocentric datum shifts , datum rotation parameters , a datum scale parameter and a value for the semimajor axis of the WGS Ellipsoid . Eight solutions were made with the various sets of input data , both from an investigative point of view and also because of the limited number of unknowns which could be solved for in any individual solution due to computer limitations . Selected Doppler satellite tracking and astro - geodetic datum orientation stations were included in the various solutions . Based on these results and other related studies accomplished by the Committee , an a - value of 6 378 135 meters and a flattening of 1 / 298 . 26 were adopted . In the development of local - to WGS 72 datum shifts , results from different geodetic disciplines were investigated , analyzed and compared . Those shifts adopted were based primarily on a large number of Doppler TRANET and GEOCEIVER station coordinates which were available worldwide . These coordinates had been determined using the Doppler point positioning method . A new World Geodetic System : WGS 84 . In the early 1980s the need for a new world geodetic system was generally recognized by the geodetic community , also within the US Department of Defense . WGS 72 no longer provided sufficient data , information , geographic coverage , or product accuracy for all then - current and anticipated applications . The means for producing a new WGS were available in the form of improved data , increased data coverage , new data types and improved techniques . GRS 80 parameters together with available Doppler , satellite laser ranging and Very Long Baseline Interferometry ( VLBI ) observations constituted significant new information . An outstanding new source of data had become available from satellite radar altimetry . Also available was an advanced least squares method called collocation which allowed for a consistent combination solution from different types of measurements all relative to the Earth ' s gravity field , i . e . geoid , gravity anomalies , deflections , dynamic Doppler , etc . The new World Geodetic System was called WGS 84 . It is currently the reference system being used by the Global Positioning System . It is geocentric and globally consistent within ±1 m . Current geodetic realizations of the geocentric reference system family International Terrestrial Reference System ( ITRS ) maintained by the IERS are geocentric , and internally consistent , at the few - cm level , while still being metre - level consistent with WGS 84 . The WGS 84 originally used the GRS 80 reference ellipsoid , but has undergone some minor refinements in later editions since its initial publication . Most of these refinements are important for high - precision orbital calculations for satellites but have little practical effect on typical topographical uses . The following table lists the primary ellipsoid parameters . The very small difference in the flattening thus results in a tiny difference of 0 . 105 mm in the semi polar axis . Longitudes on WGS 84 . WGS 84 uses the IERS Reference Meridian as defined by the Bureau International de l ' Heure , which was defined by compilation of star observations in different countries . The mean of this data caused a shift of about 100 metres east away from the Prime Meridian at Greenwich , UK . The longitude positions on WGS 84 agree with those on the older North American Datum 1927 at roughly 85° longitude west , in the east - central United States . Updates and new standards . The latest major revision of WGS 84 is also referred to as " Earth Gravitational Model 1996 " ( EGM96 ) , first published in 1996 , with revisions as recent as 2004 . This model has the same reference ellipsoid as WGS 84 , but has a higher - fidelity geoid ( roughly 100 km resolution versus 200 km for the original WGS 84 ) . Many of the original authors of WGS 84 contributed to a new higher fidelity model , called EGM2008 . This new model will have a geoid with a resolution approaching 10 km , requiring over 4 . 6 million terms in the spherical expansion ( versus 130 , 317 in EGM96 and 32 , 757 in WGS 84 ) .