Longitude is a geographic coordinate that specifies the east–west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians are imaginary semicircular lines running from pole to pole that connect points with the same longitude. The prime meridian defines 0° longitude; by convention the International Reference Meridian for the Earth passes near the Royal Observatory in Greenwich, south-east London on the island of Great Britain. Positive longitudes are east of the prime meridian, and negative ones are west.
The geographic coordinate system (GCS) is a spherical or geodetic coordinate system for measuring and communicating positions directly on the Earth as latitude and longitude. It is the simplest, oldest and most widely used of the various spatial reference systems that are in use, and forms the basis for most others. Although latitude and longitude form a coordinate tuple like a cartesian coordinate system, the geographic coordinate system is not cartesian because the measurements are angles and are not on a planar surface.
A prime meridian is an arbitrarily-chosen meridian in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian form a great circle. This great circle divides a spheroid, like Earth, into two hemispheres: the Eastern Hemisphere and the Western Hemisphere. For Earth's prime meridian, various conventions have been used or advocated in different regions throughout history. Earth's current international standard prime meridian is the IERS Reference Meridian. It is derived, but differs slightly, from the Greenwich Meridian, the previous standard.
The Western Hemisphere is the half of the planet Earth that lies west of the Prime Meridian and east of the 180th meridian. The other half is called the Eastern Hemisphere. Geo-politically, the term Western Hemisphere is often used as a metonym for the Americas or the "New World", even though geographically the hemisphere also includes parts of other continents.
A circle of latitude or line of latitude on Earth is an abstract east–west small circle connecting all locations around Earth at a given latitude coordinate line.
The "Old World" is a term for Afro-Eurasia that originated in Europe c. 1493, after Europeans had become aware of the existence of the Americas. It is used to contrast the continents of Africa, Europe, and Asia in the Eastern Hemisphere, previously thought of by their inhabitants as comprising the entire world, with the "New World", a term for the newly encountered lands of the Western Hemisphere, particularly the Americas. While located closer to Afro-Eurasia within the Eastern Hemisphere, Australia is considered neither an Old World nor a New World land, since it was only discovered by Europeans after the distinction had been made; both Australia and Antarctica were associated instead with the Terra Australis that had been posited as a hypothetical southern continent.
The Southern Hemisphere is the half (hemisphere) of Earth that is south of the Equator. It contains all or parts of five continents and four oceans, as well as New Zealand and most of the Pacific Islands in Oceania. Its surface is 80.9% water, compared with 60.7% water in the Northern Hemisphere, and it contains 32.7% of Earth's land.
A landmass, or land mass, is a large region or area of land that is in one piece and not broken up by oceans. The term is often used to refer to lands surrounded by an ocean or sea, such as a continent or a large island. In the field of geology, a landmass is a defined section of continental crust extending above sea level.
In geography and geodesy, a meridian is the locus connecting points of equal longitude, which is the angle east or west of a given prime meridian. In other words, it is a line of longitude. The position of a point along the meridian is given by that longitude and its latitude, measured in angular degrees north or south of the Equator. On a Mercator projection or on a Gall-Peters projection, each meridian is perpendicular to all circles of latitude. A meridian is half of a great circle on Earth's surface. The length of a meridian on a modern ellipsoid model of Earth has been estimated as 20,003.93 km (12,429.87 mi).
ISO 6709, Standard representation of geographic point location by coordinates, is the international standard for representation of latitude, longitude and altitude for geographic point locations.
This is a list of the extreme points of Eurasia, the points that are farther north, south, east or west than any other location on the continent. Some of these locations are open to debate, owing to the diverse definitions of Europe and Asia.
The 30th parallel north is a circle of latitude that is 30 degrees north of the Earth's equatorial plane. It stands one-third of the way between the equator and the North Pole and crosses Africa, Asia, the Pacific Ocean, North America and the Atlantic Ocean. The parallel is used in some contexts to delineate Europe or what is associated with the continent of Europe as a southernmost limit, e.g. to qualify for membership of the European Broadcasting Union.
The 180th meridian or antimeridian is the meridian 180° both east and west of the prime meridian in a geographical coordinate system. The longitude at this line can be given as either east or west.
The meridian 90° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Indian Ocean, the Southern Ocean, and Antarctica to the South Pole.
Afro-Eurasia is a landmass comprising the continents of Africa, Asia, and Europe. The terms are compound words of the names of its constituent parts. Afro-Eurasia has also been called the "Old World", in contrast to the "New World" referring to the Americas.
Eurasia is the largest continental area on Earth, comprising all of Europe and Asia. According to some geographers, physiographically, Eurasia is a single continent. The concepts of Europe and Asia as distinct continents date back to antiquity, but their borders have historically been subject to change, for example to the ancient Greeks Asia originally included Africa but they classified Europe as separate land. Eurasia is connected to Africa at the Suez Canal, and the two are sometimes combined to describe the largest contiguous landmass on Earth, Afro-Eurasia.
The borders of the oceans are the limits of Earth's oceanic waters. The definition and number of oceans can vary depending on the adopted criteria. The principal divisions of the five oceans are the Pacific Ocean, Atlantic Ocean, Indian Ocean, Southern (Antarctic) Ocean, and Arctic Ocean. Smaller regions of the oceans are called seas, gulfs, bays, straits, and other terms. Geologically, an ocean is an area of oceanic crust covered by water.
In geography and cartography, hemispheres of Earth are any division of the globe into two equal halves (hemispheres), typically divided into northern and southern halves by the equator or into western and eastern halves by an imaginary line passing through the poles. Hemispheres can be divided geographically, culturally, religiously, or based on prominent geographic features. Understanding these divisions is essential for studying Earth's geographic distribution, cultural differences, and the prominence of various geographic features.
The IERS Reference Meridian (IRM), also called the International Reference Meridian, is the prime meridian maintained by the International Earth Rotation and Reference Systems Service (IERS). It passes about 5.3 arcseconds east of George Biddell Airy's 1851 transit circle which is 102 metres (335 ft) at the latitude of the Royal Observatory, Greenwich. Thus it differs slightly from the historical Greenwich meridian.
A planetary coordinate system is a generalization of the geographic, geodetic, and the geocentric coordinate systems for planets other than Earth. Similar coordinate systems are defined for other solid celestial bodies, such as in the selenographic coordinates for the Moon. The coordinate systems for almost all of the solid bodies in the Solar System were established by Merton E. Davies of the Rand Corporation, including Mercury, Venus, Mars, the four Galilean moons of Jupiter, and Triton, the largest moon of Neptune.
