A geographic coordinate system is a coordinate system that enables every location on Earth to be specified by a set of numbers, letters or symbols. The coordinates are chosen such that one of the numbers represents a vertical position and two or three of the numbers represent a horizontal position. A common choice of coordinates is latitude and elevation. To specify a location on a plane requires a map projection; the invention of a geographic coordinate system is credited to Eratosthenes of Cyrene, who composed his now-lost Geography at the Library of Alexandria in the 3rd century BC. A century Hipparchus of Nicaea improved on this system by determining latitude from stellar measurements rather than solar altitude and determining longitude by timings of lunar eclipses, rather than dead reckoning. In the 1st or 2nd century, Marinus of Tyre compiled an extensive gazetteer and mathematically-plotted world map using coordinates measured east from a prime meridian at the westernmost known land, designated the Fortunate Isles, off the coast of western Africa around the Canary or Cape Verde Islands, measured north or south of the island of Rhodes off Asia Minor.
Ptolemy credited him with the full adoption of longitude and latitude, rather than measuring latitude in terms of the length of the midsummer day. Ptolemy's 2nd-century Geography used the same prime meridian but measured latitude from the Equator instead. After their work was translated into Arabic in the 9th century, Al-Khwārizmī's Book of the Description of the Earth corrected Marinus' and Ptolemy's errors regarding the length of the Mediterranean Sea, causing medieval Arabic cartography to use a prime meridian around 10° east of Ptolemy's line. Mathematical cartography resumed in Europe following Maximus Planudes' recovery of Ptolemy's text a little before 1300. In 1884, the United States hosted the International Meridian Conference, attended by representatives from twenty-five nations. Twenty-two of them agreed to adopt the longitude of the Royal Observatory in Greenwich, England as the zero-reference line; the Dominican Republic voted against the motion, while Brazil abstained. France adopted Greenwich Mean Time in place of local determinations by the Paris Observatory in 1911.
In order to be unambiguous about the direction of "vertical" and the "horizontal" surface above which they are measuring, map-makers choose a reference ellipsoid with a given origin and orientation that best fits their need for the area to be mapped. They choose the most appropriate mapping of the spherical coordinate system onto that ellipsoid, called a terrestrial reference system or geodetic datum. Datums may be global, meaning that they represent the whole Earth, or they may be local, meaning that they represent an ellipsoid best-fit to only a portion of the Earth. Points on the Earth's surface move relative to each other due to continental plate motion and diurnal Earth tidal movement caused by the Moon and the Sun; this daily movement can be as much as a meter. Continental movement can be up to 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 rising by only 0.2 cm.
These changes are insignificant if a local datum is used, but are statistically significant if a global datum is used. Examples of global datums include World Geodetic System, the default datum used for the Global Positioning System, the International Terrestrial Reference Frame, used for estimating continental drift and crustal deformation; the distance to Earth's center can be used both for deep positions and for positions in space. Local datums chosen by a national cartographical organisation include the North American Datum, the European ED50, the British OSGB36. Given a location, the datum provides the latitude ϕ and longitude λ. In the United Kingdom there are three common latitude and height systems in use. WGS 84 differs at Greenwich from the one used on published maps OSGB36 by 112 m; the military system ED50, used by NATO, differs from about 120 m to 180 m. The latitude and longitude on a map made against a local datum may not be the same as one obtained from a GPS receiver. Converting coordinates from one datum to another requires a datum transformation such as a Helmert transformation, although in certain situations a simple translation may be sufficient.
In popular GIS software, data projected in latitude/longitude is 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'; the "latitude" of a point on Earth's surface is the angle between the equatorial plane and the straight line that passes through that point and through the center of the Earth. Lines joining points of the same latitude trace circles on the surface of Earth called parallels, as they are parallel to the Equator and to each other; the North Pole is 90° N. The 0° parallel of latitude is designated the Equator, the fundamental plane of all geographic coordinate systems; the Equator divides the globe into Southern Hemispheres. The "longitude" of a point on Earth's surface is the angle east or west of a reference meridian to another meridian that passes through that point. All meridians are halve
John Martin is an English footballer, last attached to Isthmian League Division One North club Harlow Town. Martin began his career with Leyton Orient, making over 90 Football League appearances, before dropping into non-League football with Farnborough Town, Grays Athletic and Stevenage Borough. During the 2007–08 season, Martin enjoyed a successful first season featuring in the centre of midfield for Stevenage Borough. However, the arrival of new manager Graham Westley saw Martin fall out of favour and his first-team chances were limited. In February 2009, he was loaned out to Ebbsfleet United. Martin was recalled by manager Westley on 7 April 2009, playing a vital role in the two wins against Cambridge United and Ebbsfleet United; the latter was to be his last performance for Stevenage and on 20 May 2009, Martin was released by Stevenage Borough. On 7 August, it was announced that Martin had joined Essex based Conference South outfit Chelmsford City. Martin's stay lasted two seasons, as he was released by the club in May 2011.
He went on to join Isthmian League Division One North club Harlow Town in January 2012, making his début in the 1–0 away win over Maldon & Tiptree on 21 January. However, Martin left Harlow after playing three games for them up to 18 February. FA Trophy: 2005, 2006 Conference South: 2005 John Martin at Soccerbase John Martin at Soccerbase John Martin at Soccerbase
Gmina Niedźwiada is a rural gmina in Lubartów County, Lublin Voivodeship, in eastern Poland. Its seat is the village of Niedźwiada, which lies 10 kilometres north-east of Lubartów and 34 km north of the regional capital Lublin; the gmina covers an area of 95.82 square kilometres, as of 2006 its total population is 6,334. Gmina Niedźwiada contains the villages and settlements of Berejów, Brzeźnica Bychawska, Brzeźnica Bychawska-Kolonia, Brzeźnica Książęca, Brzeźnica Książęca-Kolonia, Brzeźnica Leśna, Górka Lubartowska, Klementynów, Niedźwiada, Niedźwiada-Kolonia, Pałecznica, Pałecznica-Kolonia, Tarło, Tarło-Kolonia and Zabiele-Kolonia. Gmina Niedźwiada is bordered by the town of Lubartów and by the gminas of Lubartów, Ostrów Lubelski, Ostrówek, Parczew and Siemień. Polish official population figures 2006 Description at www.rootsweb.com