"practice to use a nation's capital as the starting point, but other locations were also used. While British cartographers had long used the Greenwich meridian in London, other references were used elsewhere, including El Hierro, Rome, Copenhagen, Jerusalem, Saint Petersburg, Pisa, Paris (see the article ""Paris meridian""), Philadelphia, and Washington D.C. In 1884 the International Meridian Conference adopted the Greenwich meridian as the ""universal Prime Meridian"" or ""zero point of longitude"". Longitude is given as an angular measurement ranging from 0° at the Prime Meridian to +180° eastward and −180° westward. The Greek letter λ (lambda), is used to denote"
"Longitude Longitude (, ), is a geographic coordinate that specifies the east–west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians (lines running from pole to pole) connect points with the same longitude. By convention, one of these, the Prime Meridian, which passes through the Royal Observatory, Greenwich, England, was allocated the position of 0° longitude. The longitude of other places is measured as the angle east or west from the Prime Meridian, ranging from 0° at the Prime Meridian to +180° eastward"
"Lubber line A lubber line is a fixed line on a compass binnacle or radar plan position indicator display pointing towards the front of the ship or aircraft and corresponding to the craft's centerline (being the customary direction of movement). The line represents 0 degrees and is therefore the zero-point from which relative bearings are measured, e.g., """"twenty-degrees to port"""". Compasses on sailboats may have additional lubber lines at forty-five degrees from the centerline. This represents about as close to the wind as the average boat will sail. These lubber lines may be used when sailing close hauled to see"
"Null Island Null Island is a name for the area around the point where the prime meridian and the equator cross; in the WGS84 datum, this is at zero degrees latitude and longitude [.] (the location is in the Gulf of Guinea off the west African coast). The name 'Null Island' serves as both a joke based around the suppositional existence of an island there (in reality, only a buoy [pictured] exists there), and also as a name to which coordinates erroneously set to 0,0 are assigned in placenames databases in order to more easily find and fix them. The"
"Latitude In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earth's surface. Latitude is an angle (defined below) which ranges from 0° at the Equator to 90° (North or South) at the poles. Lines of constant latitude, or ""parallels"", run east–west as circles parallel to the equator. Latitude is used together with longitude to specify the precise location of features on the surface of the Earth. On its own, the term latitude should be taken to be the ""geodetic latitude"" as defined below. Briefly, geodetic latitude at a point is the angle"
"becoming greater than 45 degrees) you are being headed, and should consider tacking. Directional Gyros on aircraft also have additional forty-five degree lubber lines. These are useful for intercepting tracks and making procedure turns. Lubber line A lubber line is a fixed line on a compass binnacle or radar plan position indicator display pointing towards the front of the ship or aircraft and corresponding to the craft's centerline (being the customary direction of movement). The line represents 0 degrees and is therefore the zero-point from which relative bearings are measured, e.g., """"twenty-degrees to port"""". Compasses on sailboats may have additional"
"Isotropic line In the geometry of quadratic forms, an isotropic line or null line is a line for which the quadratic form applied to the displacement vector between any pair of its points is zero. An isotropic line occurs only with an isotropic quadratic form, and never with a definite quadratic form. Using complex geometry, Edmond Laguerre first suggested the existence of two isotropic lines through the point that depend on the imaginary unit : Laguerre then interpreted these lines as geodesics: In the complex projective plane, points are represented by homogeneous coordinates formula_3 and lines by homogeneous coordinates formula_4."
"Meridian (geography) A (geographical) meridian (or line of longitude) is the half of an imaginary great circle on the Earth's surface, terminated by the North Pole and the South Pole, connecting points of equal longitude, as measured in angular degrees east or west of the Prime Meridian. 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. Each meridian is perpendicular to all circles of latitude. Each is also the same length, being half of a great circle on the Earth's surface and therefore"
"(negative dip). The range of dip is from -90 degrees (at the South Magnetic Pole) to +90 degrees (at the North Magnetic Pole). Contour lines along which the dip measured at the Earth's surface is equal are referred to as isoclinic lines. The locus of the points having zero dip is called the ""magnetic equator"" or aclinic line. The phenomenon is especially important in aviation, as it causes the airplane's compass to give erroneous readings during banked turns and airspeed changes. The latter errors occur because the compass card tilts on its mount when under acceleration. Compass needles are often"
"line."" For isotropic lines through the origin, a particular point is a null vector, and the collection of all such isotropic lines forms the light cone at the origin. Élie Cartan expanded the concept of isotropic lines to multivectors in his book on spinors in three dimensions. Isotropic line In the geometry of quadratic forms, an isotropic line or null line is a line for which the quadratic form applied to the displacement vector between any pair of its points is zero. An isotropic line occurs only with an isotropic quadratic form, and never with a definite quadratic form. Using"
"it in several places for political reasons, including between far eastern Russia and the far western Aleutian Islands. The combination of these two components specifies the position of any location on the surface of Earth, without consideration of altitude or depth. The grid formed by lines of latitude and longitude is known as a ""graticule"". The origin/zero point of this system is located in the Gulf of Guinea about south of Tema, Ghana. On the GRS80 or WGS84 spheroid at sea level at the Equator, one latitudinal second measures ""30.715 metres"", one latitudinal minute is ""1843 metres"" and one latitudinal"
"observation buoy, part of the PIRATA system operated jointly by the United States, France, and Brazil. The depth at this place is around . Null Island Null Island is a name for the area around the point where the prime meridian and the equator cross; in the WGS84 datum, this is at zero degrees latitude and longitude [.] (the location is in the Gulf of Guinea off the west African coast). The name 'Null Island' serves as both a joke based around the suppositional existence of an island there (in reality, only a buoy [pictured] exists there), and also as"
"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 South Pole is 90° S. The 0° parallel of latitude is designated the Equator, the fundamental plane of all geographic coordinate systems. The Equator divides the globe into Northern and Southern Hemispheres. The ""longitude"" (abbreviation: Long., λ, or lambda) 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 halves of great"
"(or geostationary Earth orbit/GEO) is a geosynchronous orbit directly above the Earth's equator (0° latitude), with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero (i.e. ""circular orbit""). An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers. Communications satellites and weather satellites are often given geostationary orbits, so that the satellite antennas that communicate with them do not have to move to track them, but can be pointed permanently at the position in the sky where they stay. Due to the constant 0° latitude and"
"Equator An equator of a rotating spheroid (such as a planet) is its zeroth circle of latitude (parallel). It is the imaginary line on the spheroid's surface, equidistant from its poles, dividing it into northern and southern hemispheres. In other words, it is the intersection of the spheroid's surface with the plane perpendicular to its axis of rotation and midway between its geographical poles. On Earth, ""the Equator"" is about long, of which 78.8% lies across water and 21.3% over land. Indonesia is the country straddling the greatest length of the equatorial line across both land and sea. The name"
"is derived from medieval Latin word ""aequator"", in the phrase ""circulus aequator diei et noctis,"" meaning ‘circle equalizing day and night’, from the Latin word ""aequare"" meaning ‘make equal’. The latitude of the Earth's equator is, by definition, 0° (zero degrees) of arc. The Equator is one of the five notable circles of latitude on Earth; the other four are both polar circles (the Arctic Circle and the Antarctic Circle) and both tropical circles (the Tropic of Cancer and the Tropic of Capricorn). The Equator is the only line of latitude which is also a great circle — that is,"
"Prime meridian A prime meridian is a meridian (a line of longitude) in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its antimeridian (the 180th meridian in a 360°-system) form a great circle. This great circle divides the sphere, e.g., Earth, into two hemispheres. If one uses directions of East and West from a defined prime meridian, then they can be called the Eastern Hemisphere and the Western Hemisphere. A prime meridian is ultimately arbitrary, unlike an equator, which is determined by the axis of rotation—and various conventions have been used"
"be negative and only S may have a fractional value. Decimal degrees Decimal degrees (DD) express latitude and longitude geographic coordinates as decimal fractions and are used in many geographic information systems (GIS), web mapping applications such as OpenStreetMap, and GPS devices. Decimal degrees are an alternative to using degrees, minutes, and seconds (DMS). As with latitude and longitude, the values are bounded by ±90° and ±180° respectively. Positive latitudes are north of the equator, negative latitudes are south of the equator. Positive longitudes are east of Prime Meridian, negative longitudes are west of the Prime Meridian. Latitude and longitude"
"of Mars (since about 2002) is to use planetocentric coordinates. The meridian of Mars is located at Airy-0 crater. Tidally-locked bodies have a natural reference longitude passing through the point nearest to their parent body: 0° the center of the primary-facing hemisphere, 90° the center of the leading hemisphere, 180° the center of the anti-primary hemisphere, and 270° the center of the trailing hemisphere. However, libration due to non-circular orbits or axial tilts causes this point to move around any fixed point on the celestial body like an analemma. Longitude Longitude (, ), is a geographic coordinate that specifies the"
"strip is indeed at ""astronomical"" longitude zero degrees, zero minutes, and zero seconds—but GPS receivers show ""geodetic"" longitude, which equalises the higher mass, otherwise seen, of the eastern hemisphere (specifically per Standard ITRF/WGS 84). Before the establishment of a common meridian, most maritime countries established their own prime meridian, usually passing through the country in question. In 1721, Great Britain established its own meridian passing through an early transit circle at the newly established Royal Observatory at Greenwich. The meridian was moved around 10 metres or so east on three occasions as transit circles with newer and better instruments were"
"has coordinates: Horizontal and vertical lines In the general equation of a line, ""ax"" + ""by"" + ""c"" = 0, ""a"" and ""b"" cannot both be zero unless ""c"" is also zero, in which case the equation does not define a line. If ""a"" = 0 and ""b"" 0, the line is horizontal and has equation ""y"" = -""c""/""b"". The distance from (""x"", ""y"") to this line is measured along a vertical line segment of length |""y"" - (-""c""/""b"")| = |""by"" + ""c""| / |""b""| in accordance with the formula. Similarly, for vertical lines (""b"" = 0) the distance between"
"Line (geometry) The notion of line or straight line was introduced by ancient mathematicians to represent straight objects (i.e., having no curvature) with negligible width and depth. Lines are an idealization of such objects. Until the 17th century, lines were defined as the ""[…] first species of quantity, which has only one dimension, namely length, without any width nor depth, and is nothing else than the flow or run of the point which […] will leave from its imaginary moving some vestige in length, exempt of any width. […] The straight line is that which is equally extended between its"
"sometimes known as null in mathematics. The location is used by mapping systems to trap errors. Such errors arise, for example, where an image artifact is erroneously associated to the location by software which cannot attribute a geo-position, and instead associates a latitude and longitude of ""Null,Null"" or ""0,0"". Other data mapped to the location include activity events from the Strava fitness-tracking app, apparently (as reported in January 2018 by Bellingcat) mapped to the location due to users entering ""0,0"" coordinates to disguise their real location. The only actual non-oceanic feature in that region is a moored weather and sea"
"scientists determined that in the Ordnance Survey system the longitude of the international Greenwich meridian was not 0° but 0°00'00.417"" (about 8 m) East. Besides the change of the reference line, imperfections of the surveying system added another discrepancy to the definition of the origin, so that the Bradley line itself is now 0°00'00.12"" East of the Ordnance Survey Zero Meridian (about 2.3m). This old astronomical prime meridian has been replaced by a more precise prime meridian. When Greenwich was an active observatory, geographical coordinates were referred to a local oblate spheroid called a datum known as a geoid, whose"
"Identity line In a 2-dimensional Cartesian coordinate system, with ""x"" representing the abscissa and ""y"" the ordinate, the identity line or line of equality is the ""y"" = ""x"" line. The line, sometimes called the 1:1 line, has a slope of 1. When the abscissa and ordinate are on the same scale, the identity line forms a 45° angle with the abscissa, and is thus also, informally, called the 45° line. The line is often used as a reference in a 2-dimensional scatter plot comparing two sets of data expected to be identical under ideal conditions. When the corresponding data"
": ""db"" : ""dc"") for all nonzero values of ""d"". Hence a different equation of the same line ""dax"" + ""dby"" + ""dcz"" = 0 gives the same homogeneous coordinates. A point [""x"" : ""y"" : ""z""] lies on a line (""a"" : ""b"" : ""c"") if ""ax"" + ""by"" + ""cz"" = 0. Therefore, lines with coordinates (""a"" : ""b"" : ""c"") where ""a"", ""b"" are not both 0 correspond to the lines in the usual real plane, because they contain points that are not at infinity. The line with coordinates (0 : 0 : 1) is the line"
"time at zero longitude (see Greenwich Mean Time). Reliable marine chronometers were unavailable until the late 18th century and not affordable until the 19th century. For about a hundred years, from about 1767 until about 1850, mariners lacking a chronometer used the method of lunar distances to determine Greenwich time to find their longitude. A mariner with a chronometer could check its reading using a lunar determination of Greenwich time. In navigation, a rhumb line (or loxodrome) is a line crossing all meridians of longitude at the same angle, i.e. a path derived from a defined initial bearing. That is,"
"Airy-0 Airy-0 is a crater on Mars whose location defined the position of the prime meridian of that planet. It is about across and lies within the larger crater Airy in the region Sinus Meridiani. The IAU Working Group on Cartographic Coordinates and Rotational Elements has now recommended setting the longitude of the Viking 1 lander (47°.95137 west) as the standard. This deﬁnition maintains the position of the center of Airy-0 at 0° longitude, within the tolerance of current cartographic uncertainties. Merton Davies tied this crater into an extensive geodetic control network of the planet Mars based on Mariner 9"
"[""m""]. (If ""K"" is the unknot, then [""l""] is a power of [""m""], and a peripheral subgroup is generated by [""m""] alone.) A longitude is a loop that runs from the basepoint ""x"" along a path γ to a point ""y"" on the boundary of a tubular neighborhood of ""K"", then follows ""along"" the tube, making one full lap to return to ""y"", then returns to ""x"" via γ. A meridian is a loop that runs from ""x"" to ""y"", then circles ""around"" the tube, returns to ""y"", then returns to ""x"". (The property of being a longitude or meridian"
"averages out. Astronomical latitude is not to be confused with declination, the coordinate astronomers use in a similar way to specify the angular position of stars north/south of the celestial equator (see equatorial coordinates), nor with ecliptic latitude, the coordinate that astronomers use to specify the angular position of stars north/south of the ecliptic (see ecliptic coordinates). Latitude In geography, latitude is a geographic coordinate that specifies the north–south position of a point on the Earth's surface. Latitude is an angle (defined below) which ranges from 0° at the Equator to 90° (North or South) at the poles. Lines of"
"""a"", ""b"" and ""f"". They are listed in ellipse. A primary use of reference ellipsoids is to serve as a basis for a coordinate system of latitude (north/south), longitude (east/west), and ellipsoidal height. For this purpose it is necessary to identify a ""zero meridian"", which for Earth is usually the Prime Meridian. For other bodies a fixed surface feature is usually referenced, which for Mars is the meridian passing through the crater Airy-0. It is possible for many different coordinate systems to be defined upon the same reference ellipsoid. The longitude measures the rotational angle between the zero meridian and"
"Decimal degrees Decimal degrees (DD) express latitude and longitude geographic coordinates as decimal fractions and are used in many geographic information systems (GIS), web mapping applications such as OpenStreetMap, and GPS devices. Decimal degrees are an alternative to using degrees, minutes, and seconds (DMS). As with latitude and longitude, the values are bounded by ±90° and ±180° respectively. Positive latitudes are north of the equator, negative latitudes are south of the equator. Positive longitudes are east of Prime Meridian, negative longitudes are west of the Prime Meridian. Latitude and longitude are usually expressed in that sequence, latitude before longitude. The"
"degree is ""110.6 kilometres"". The circles of longitude, meridians, meet at the geographical poles, with the west-east width of a second naturally decreasing as latitude increases. On the Equator at sea level, one longitudinal second measures ""30.92 metres"", a longitudinal minute is ""1855 metres"" and a longitudinal degree is ""111.3 kilometres"". At 30° a longitudinal second is ""26.76 metres"", at Greenwich (51°28′38″N) ""19.22 metres"", and at 60° it is ""15.42 metres"". On the WGS84 spheroid, the length in meters of a degree of latitude at latitude φ (that is, the distance along a north–south line from latitude (φ − 0.5)"