Geographic coordinate system
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 they are mapping. 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 metre. 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. Coordinates from the mapping system can sometimes be changed into another datum using a simple translation.
For example, to convert from ETRF89 to the Irish Grid add 49 metres to the east, subtract 23.4 metres from the north. More one datum is changed into any other datum using a process called Helmert transformations; this involves converting the spherical coordinates into Cartesian coordinates and applying a seven parameter transformation, converting back. 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 fun
A time zone is a region of the globe that observes a uniform standard time for legal and social purposes. Time zones tend to follow the boundaries of countries and their subdivisions because it is convenient for areas in close commercial or other communication to keep the same time. Most of the time zones on land are offset from Coordinated Universal Time by a whole number of hours, but a few zones are offset by 30 or 45 minutes; some higher latitude and temperate zone countries use daylight saving time for part of the year by adjusting local clock time by an hour. Many land time zones are skewed toward the west of the corresponding nautical time zones; this creates a permanent daylight saving time effect. Before clocks were first invented, it was common practice to mark the time of day with apparent solar time – for example, the time on a sundial –, different for every location and dependent on longitude; when well-regulated mechanical clocks became widespread in the early 19th century, each city began to use some local mean solar time.
Apparent and mean solar time can differ by up to around 15 minutes because of the elliptical shape of the Earth's orbit around the Sun and the tilt of the Earth's axis. Mean solar time has days of equal length, the difference between the two sums to zero after a year. Greenwich Mean Time was established in 1675, when the Royal Observatory was built, as an aid to mariners to determine longitude at sea, providing a standard reference time while each city in England kept a different local time. Local solar time became inconvenient as rail transport and telecommunications improved, because clocks differed between places by amounts corresponding to the differences in their geographical longitudes, which varied by four minutes of time for every degree of longitude. For example, Bristol is about 2.5 degrees west of Greenwich, so when it is solar noon in Bristol, it is about 10 minutes past solar noon in London. The use of time zones accumulates these differences into longer units hours, so that nearby places can share a common standard for timekeeping.
The first adoption of a standard time was on December 1, 1847, in Great Britain by railway companies using GMT kept by portable chronometers. The first of these companies to adopt standard time was the Great Western Railway in November 1840; this became known as Railway Time. About August 23, 1852, time signals were first transmitted by telegraph from the Royal Observatory, Greenwich. Though 98% of Great Britain's public clocks were using GMT by 1855, it was not made Britain's legal time until August 2, 1880; some British clocks from this period have two minute hands—one for the local time, one for GMT. Improvements in worldwide communication further increased the need for interacting parties to communicate mutually comprehensible time references to one another; the problem of differing local times could be solved across larger areas by synchronizing clocks worldwide, but in many places that adopted time would differ markedly from the solar time to which people were accustomed. On November 2, 1868, the British colony of New Zealand adopted a standard time to be observed throughout the colony, was the first country to do so.
It was based on the longitude 172°30′ East of Greenwich, 11 hours 30 minutes ahead of GMT. This standard was known as New Zealand Mean Time. Timekeeping on the American railroads in the mid-19th century was somewhat confused; each railroad used its own standard time based on the local time of its headquarters or most important terminus, the railroad's train schedules were published using its own time. Some junctions served by several railroads had a clock for each railroad, each showing a different time. Charles F. Dowd proposed a system of one-hour standard time zones for American railroads about 1863, although he published nothing on the matter at that time and did not consult railroad officials until 1869. In 1870 he proposed four ideal time zones, the first centered on Washington, D. C. but by 1872 the first was centered with geographic borders. Dowd's system was never accepted by American railroads. Instead, U. S. and Canadian railroads implemented a version proposed by William F. Allen, the editor of the Traveler's Official Railway Guide.
The borders of its time zones ran through railroad stations in major cities. For example, the border between its Eastern and Central time zones ran through Detroit, Pittsburgh and Charleston, it was inaugurated on Sunday, November 18, 1883 called "The Day of Two Noons", when each railroad station clock was reset as standard-time noon was reached within each time zone. The zones were named Intercolonial, Central and Pacific. Within a year 85% of all cities with populations over 10,000, about 200 cities, were using standard time. A notable exception was Detroit which kept local time until 1900 tried Central Standard Time, local mean time, Eastern Standard Time before a May 1915 ordinance settled on EST and was ratified by popular vote in August 1916; the confusion of times came to an end when Standard zone time was formally adopted by the U. S. Congress in the Standard Time Act of March 19, 1918; the first known person to conceive of a worldwide system of time zones was the Italian mathematician
Buenos Aires is the capital and largest city of Argentina. The city is located on the western shore of the estuary of the Río de la Plata, on the South American continent's southeastern coast. "Buenos Aires" can be translated as "fair winds" or "good airs", but the former was the meaning intended by the founders in the 16th century, by the use of the original name "Real de Nuestra Señora Santa María del Buen Ayre". The Greater Buenos Aires conurbation, which includes several Buenos Aires Province districts, constitutes the fourth-most populous metropolitan area in the Americas, with a population of around 15.6 million. The city of Buenos Aires is the Province's capital. In 1880, after decades of political infighting, Buenos Aires was federalized and removed from Buenos Aires Province; the city limits were enlarged to include the towns of Flores. The 1994 constitutional amendment granted the city autonomy, hence its formal name: Autonomous City of Buenos Aires, its citizens first elected a chief of government in 1996.
Buenos Aires is considered an'alpha city' by the study GaWC5. Buenos Aires' quality of life was ranked 91st in the world, being one of the best in Latin America in 2018, it is the most visited city in South America, the second-most visited city of Latin America. Buenos Aires is a top tourist destination, is known for its preserved Eclectic European architecture and rich cultural life. Buenos Aires held the 1st Pan American Games in 1951 as well as hosting two venues in the 1978 FIFA World Cup. Buenos Aires hosted the 2018 the 2018 G20 summit. Buenos Aires is a multicultural city, being home to multiple religious groups. Several languages are spoken in the city in addition to Spanish, contributing to its culture and the dialect spoken in the city and in some other parts of the country; this is because in the last 150 years the city, the country in general, has been a major recipient of millions of immigrants from all over the world, making it a melting pot where several ethnic groups live together and being considered one of the most diverse cities of the Americas.
It is recorded under the archives of Aragonese that Catalan missionaries and Jesuits arriving in Cagliari under the Crown of Aragon, after its capture from the Pisans in 1324 established their headquarters on top of a hill that overlooked the city. The hill was known to them as Bonaira, as it was free of the foul smell prevalent in the old city, adjacent to swampland. During the siege of Cagliari, the Catalans built a sanctuary to the Virgin Mary on top of the hill. In 1335, King Alfonso the Gentle donated the church to the Mercedarians, who built an abbey that stands to this day. In the years after that, a story circulated, claiming that a statue of the Virgin Mary was retrieved from the sea after it miraculously helped to calm a storm in the Mediterranean Sea; the statue was placed in the abbey. Spanish sailors Andalusians, venerated this image and invoked the "Fair Winds" to aid them in their navigation and prevent shipwrecks. A sanctuary to the Virgin of Buen Ayre would be erected in Seville.
In the first foundation of Buenos Aires, Spanish sailors arrived thankfully in the Río de la Plata by the blessings of the "Santa Maria de los Buenos Aires", the "Holy Virgin Mary of the Good Winds", said to have given them the good winds to reach the coast of what is today the modern city of Buenos Aires. Pedro de Mendoza called the city "Holy Mary of the Fair Winds", a name suggested by the chaplain of Mendoza's expedition – a devotee of the Virgin of Buen Ayre – after the Sardinian Madonna de Bonaria. Mendoza's settlement soon came under attack by indigenous people, was abandoned in 1541. For many years, the name was attributed to a Sancho del Campo, said to have exclaimed: How fair are the winds of this land!, as he arrived. But Eduardo Madero, in 1882 after conducting extensive research in Spanish archives concluded that the name was indeed linked with the devotion of the sailors to Our Lady of Buen Ayre. A second settlement was established in 1580 by Juan de Garay, who sailed down the Paraná River from Asunción.
Garay preserved the name chosen by Mendoza, calling the city Ciudad de la Santísima Trinidad y Puerto de Santa María del Buen Aire. The short form "Buenos Aires" became the common usage during the 17th century; the usual abbreviation for Buenos Aires in Spanish is Bs. As, it is common as well to refer to it as "B. A." or "BA". While "BA" is used more by expats residing in the city, the locals more use the abbreviation "Baires", in one word. Seaman Juan Díaz de Solís, navigating in the name of Spain, was the first European to reach the Río de la Plata in 1516, his expedition was cut short when he was killed during an attack by the native Charrúa tribe in what is now Uruguay. The city of Buenos Aires was first established as Ciudad de Nuestra Señora Santa María del Buen Ayre after Our Lady of Bonaria on 2 February 1536 by a Spanish expedition led by Pedro de Mendoza; the settlement founded by Mendoza was located in what is today the San Telmo district of Buenos Aires, south of the city centre. More attacks by the indigenous