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77-595: The Irish grid reference system is a system of geographic grid references used for paper mapping in Ireland (both Northern Ireland and the Republic of Ireland ). Any location in Ireland can be described in terms of its distance from the origin (0, 0), which lies off the southwest coast. The Irish grid partially overlaps the British grid , and uses a similar co-ordinate system but with

154-459: A truncated grid reference may be used where the general location is already known to participants and may be assumed. Because the (leading) most significant digits specify the part of the world and the (trailing) least significant digits provide a precision that is not needed in most circumstances, they may be unnecessary for some uses. This permits users to shorten the example coordinates to 949-361 by concealing 05nnn34 56nnn74 , assuming

231-407: A 1 km (0.62 mi) square) through to five (for a 1 m (3 ft 3 in)) square; the most common usage is the six figure grid reference , employing three digits in each coordinate to determine a 100 m (330 ft) square. Coordinates may also be given relative to the origin of the entire 500 by 500 km (310 by 310 mi) grid (in the format easting, northing). For example,

308-415: A 6-figure grid reference identifies a square of 100-metre sides, an 8-figure reference would identify a 10-metre square, and a 10-digit reference a 1-metre square. In order to give a standard 6-figure grid reference from a 10-figure GPS readout, the 4th, 5th, 9th and 10th digits must be omitted, so it is important not to read just the first 6 digits. Map projection In cartography , a map projection

385-458: A course of constant bearing is always plotted as a straight line. A normal cylindrical projection is any projection in which meridians are mapped to equally spaced vertical lines and circles of latitude (parallels) are mapped to horizontal lines. The mapping of meridians to vertical lines can be visualized by imagining a cylinder whose axis coincides with the Earth's axis of rotation. This cylinder

462-416: A cylindrical projection (for example) is one which: (If you rotate the globe before projecting then the parallels and meridians will not necessarily still be straight lines. Rotations are normally ignored for the purpose of classification.) Where the light source emanates along the line described in this last constraint is what yields the differences between the various "natural" cylindrical projections. But

539-458: A digit from 0 to 9 (with 0 0 being the bottom left square and 9 9 being the top right square). For the church in Little Plumpton, this gives the digits 6 and 7 (6 on the left to right axis (Eastings) and 7 on the bottom to top axis (Northings). These are added to the four-figure grid reference after the two digits describing the same coordinate axis , and thus our six-figure grid reference for

616-636: A flat surface of a map. The datum, along with a map projection applied to a grid of reference locations, establishes a grid system for plotting locations. Conformal projections are generally preferred. Common map projections include the transverse mercator (used in Universal Transverse Mercator , the British National Grid , the State Plane Coordinate System for some states), Lambert Conformal Conic (some states in

693-415: A four-digit grid reference describing a one-kilometre square on the ground. The convention is the grid reference numbers call out the lower-left corner of the desired square. In the example map above, the town Little Plumpton lies in the square 6901, even though the writing which labels the town is in 6802 and 6902, most of the buildings (the orange boxed symbols) are in square 6901. The more digits added to

770-455: A grid reference, the more precise the reference becomes. To locate a specific building in Little Plumpton, a further two digits are added to the four-digit reference to create a six-digit reference. The extra two digits describe a position within the 1-kilometre square. Imagine (or draw or superimpose a Romer ) a further 10x10 grid within the current grid square. Any of the 100 squares in the superimposed 10×10 grid can be accurately described using

847-481: A location-specific optimisation of UTM , which runs in parallel with the existing Irish grid system. In both systems, the true origin is at 53° 30' N, 8° W — a point in Lough Ree , close to the western ( Co. Roscommon ) shore, whose grid reference is N000500 . The ITM system was specified so as to provide precise alignment with modern high-precision global positioning receivers . The area of Ireland

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924-543: A map, but it is important to know how many digits the GPS displays to avoid reading off just the first six digits. A GPS unit commonly gives a ten-digit grid reference, based on two groups of five numbers for the Easting and Northing values. Each successive increase in precision (from 6 digit to 8 digit to 10 digit) pinpoints the location more precisely by a factor of 10. Since, in the UK at least,

1001-475: A meridian more suited to its westerly location. In general, neither Ireland nor Great Britain uses latitude or longitude in describing internal geographic locations. Instead grid reference systems are used for mapping. The national grid referencing system was devised by the Ordnance Survey , and is heavily used in their survey data, and in maps (whether published by the Ordnance Survey of Ireland ,

1078-416: A parallel of origin (usually written φ 0 ) are often used to define the origin of the map projection. A globe is the only way to represent the Earth with constant scale throughout the entire map in all directions. A map cannot achieve that property for any area, no matter how small. It can, however, achieve constant scale along specific lines. Some possible properties are: Projection construction

1155-399: A plane without distortion. The same applies to other reference surfaces used as models for the Earth, such as oblate spheroids , ellipsoids , and geoids . Since any map projection is a representation of one of those surfaces on a plane, all map projections distort. The classical way of showing the distortion inherent in a projection is to use Tissot's indicatrix . For a given point, using

1232-406: A proxy for the combination of angular deformation and areal inflation; such methods arbitrarily choose what paths to measure and how to weight them in order to yield a single result. Many have been described. The creation of a map projection involves two steps: Some of the simplest map projections are literal projections, as obtained by placing a light source at some definite point relative to

1309-572: A resurgence in the use of GCS. That said, projected coordinate systems are still very common in the GIS data stored in the Spatial Data Infrastructures (SDI) of local areas, such as cities, counties, states and provinces, and small countries. Because the purpose of any coordinate system is to accurately and unambiguously measure, communicate, and perform calculations on locations, it must be defined precisely. The EPSG Geodetic Parameter Dataset

1386-646: A shadow on a screen, or the rectilinear image produced by a pinhole camera on a flat film plate. Rather, any mathematical function that transforms coordinates from the curved surface distinctly and smoothly to the plane is a projection. Few projections in practical use are perspective. Most of this article assumes that the surface to be mapped is that of a sphere. The Earth and other large celestial bodies are generally better modeled as oblate spheroids , whereas small objects such as asteroids often have irregular shapes. The surfaces of planetary bodies can be mapped even if they are too irregular to be modeled well with

1463-406: A sphere on a plane necessarily distort the surface in some way. Depending on the purpose of the map, some distortions are acceptable and others are not; therefore, different map projections exist in order to preserve some properties of the sphere-like body at the expense of other properties. The study of map projections is primarily about the characterization of their distortions. There is no limit to

1540-472: A sphere or ellipsoid. Therefore, more generally, a map projection is any method of flattening a continuous curved surface onto a plane. The most well-known map projection is the Mercator projection . This map projection has the property of being conformal . However, it has been criticized throughout the 20th century for enlarging regions further from the equator. To contrast, equal-area projections such as

1617-709: Is according to properties of the model they preserve. Some of the more common categories are: Because the sphere is not a developable surface , it is impossible to construct a map projection that is both equal-area and conformal. The three developable surfaces (plane, cylinder, cone) provide useful models for understanding, describing, and developing map projections. However, these models are limited in two fundamental ways. For one thing, most world projections in use do not fall into any of those categories. For another thing, even most projections that do fall into those categories are not naturally attainable through physical projection. As L. P. Lee notes, No reference has been made in

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1694-399: Is also affected by how the shape of the Earth or planetary body is approximated. In the following section on projection categories, the earth is taken as a sphere in order to simplify the discussion. However, the Earth's actual shape is closer to an oblate ellipsoid . Whether spherical or ellipsoidal, the principles discussed hold without loss of generality. Selecting a model for a shape of

1771-442: Is any of a broad set of transformations employed to represent the curved two-dimensional surface of a globe on a plane . In a map projection, coordinates , often expressed as latitude and longitude , of locations from the surface of the globe are transformed to coordinates on a plane. Projection is a necessary step in creating a two-dimensional map and is one of the essential elements of cartography. All projections of

1848-634: Is divided into 25 squares, measuring 100 by 100 km (62 by 62 mi), each identified by a single letter. The squares are numbered A to Z with I being omitted. Seven of the squares do not actually cover any land in Ireland: A, E, K, P, U, Y and Z. Within each square, eastings and northings from the origin (south west corner) of the square are given numerically. For example, G0305 means 'square G, 3 km (1.9 mi) east, 5 km (3.1 mi) north'. A location can be indicated to varying resolutions numerically, usually from two digits in each coordinate (for

1925-534: Is given a two-digit code, based on the British national grid reference system with an origin point just off the southwest coast of the United Kingdom . The area is divided into 100 km squares, each of which is denoted by a two-letter code. Within each 100 km square, a numerical grid reference is used. Since the Eastings and Northings are one kilometre apart, a combination of a Northing and an Easting will give

2002-445: Is given by φ): In the first case (Mercator), the east-west scale always equals the north-south scale. In the second case (central cylindrical), the north-south scale exceeds the east-west scale everywhere away from the equator. Each remaining case has a pair of secant lines —a pair of identical latitudes of opposite sign (or else the equator) at which the east-west scale matches the north-south-scale. Normal cylindrical projections map

2079-436: Is the most common mechanism for publishing such definitions in a machine-readable form, and forms the basis for many GIS and other location-aware software programs. A projected SRS specification consists of three parts: To establish the position of a geographic location on a map , a map projection is used to convert geodetic coordinates to plane coordinates on a map; it projects the datum ellipsoidal coordinates and height onto

2156-401: Is through grayscale or color gradations whose shade represents the magnitude of the angular deformation or areal inflation. Sometimes both are shown simultaneously by blending two colors to create a bivariate map . To measure distortion globally across areas instead of at just a single point necessarily involves choosing priorities to reach a compromise. Some schemes use distance distortion as

2233-580: Is usually represented conventionally with easting first, northing second. For example, the peak of Mount Assiniboine (at 50°52′10″N 115°39′03″W  /  50.86944°N 115.65083°W  / 50.86944; -115.65083 on the British Columbia / Alberta border in Canada ) in UTM Zone 11 is at (0594934mE, 5636174mN) , meaning that is almost 600km east of the false origin for Zone 11 (95km east of

2310-456: Is wrapped around the Earth, projected onto, and then unrolled. By the geometry of their construction, cylindrical projections stretch distances east-west. The amount of stretch is the same at any chosen latitude on all cylindrical projections, and is given by the secant of the latitude as a multiple of the equator's scale. The various cylindrical projections are distinguished from each other solely by their north-south stretching (where latitude

2387-482: The Collignon projection in polar areas. The term "conic projection" is used to refer to any projection in which meridians are mapped to equally spaced lines radiating out from the apex and circles of latitude (parallels) are mapped to circular arcs centered on the apex. When making a conic map, the map maker arbitrarily picks two standard parallels. Those standard parallels may be visualized as secant lines where

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2464-633: The Geographic coordinate system (GCS, latitude and longitude) date to the Hellenistic period , proliferating during the Enlightenment Era of the 18th century. However, their use as the basis for specifying precise locations, rather than latitude and longitude, is a 20th century innovation. Among the earliest was the State Plane Coordinate System (SPCS), which was developed in the United States during

2541-480: The Ordnance Survey of Northern Ireland or commercial map producers) based on those surveys. Additionally grid references are commonly quoted in other publications and data sources, such as guide books or government planning documents. In 2001, the Ordnance Survey of Ireland and the Ordnance Survey of Northern Ireland jointly implemented a new coordinate system for Ireland called Irish Transverse Mercator, or ITM,

2618-497: The SPCS ), and Mercator ( Swiss coordinate system ). Map projection formulas depend on the geometry of the projection as well as parameters dependent on the particular location at which the map is projected. The set of parameters can vary based on the type of project and the conventions chosen for the projection. For the transverse Mercator projection used in UTM, the parameters associated are

2695-707: The Sinusoidal projection and the Gall–Peters projection show the correct sizes of countries relative to each other, but distort angles. The National Geographic Society and most atlases favor map projections that compromise between area and angular distortion, such as the Robinson projection and the Winkel tripel projection . Many properties can be measured on the Earth's surface independently of its geography: Map projections can be constructed to preserve some of these properties at

2772-615: The 1930s for surveying and engineering, because calculations such as distance are much simpler in a Cartesian coordinate system than the three-dimensional trigonometry of GCS. In the United Kingdom , the first version of the British National Grid was released in 1938, based on earlier experiments during World War I by the Army and the Ordnance Survey . During World War II , modern warfare practices required soldiers to quickly and accurately measure and report their location, leading to

2849-434: The 1980s with the emergence of geographic information systems . GIS requires locations to be specified as precise coordinates and performs numerous calculations on them, making cartesian geometry preferable to spherical trigonometry when computing horsepower was at a premium. In recent years, the rise of global GIS datasets and satellite navigation , along with an abundance of processing speed in personal computers, have led to

2926-454: The Earth involves choosing between the advantages and disadvantages of a sphere versus an ellipsoid. Spherical models are useful for small-scale maps such as world atlases and globes, since the error at that scale is not usually noticeable or important enough to justify using the more complicated ellipsoid. The ellipsoidal model is commonly used to construct topographic maps and for other large- and medium-scale maps that need to accurately depict

3003-597: The UK into one-kilometre squares, east of an imaginary zero point in the Atlantic Ocean, west of Cornwall. The grid lines point to a Grid North, varying slightly from True North. This variation is zero on the central meridian (north-south line) of the map, which is at two degrees West of the Prime Meridian , and greatest at the map edges. The difference between grid north and true north is very small and can be ignored for most navigation purposes. The difference exists because

3080-494: The above definitions to cylinders, cones or planes. The projections are termed cylindric or conic because they can be regarded as developed on a cylinder or a cone, as the case may be, but it is as well to dispense with picturing cylinders and cones, since they have given rise to much misunderstanding. Particularly is this so with regard to the conic projections with two standard parallels: they may be regarded as developed on cones, but they are cones which bear no simple relationship to

3157-598: The alphanumeric Military Grid Reference System (MGRS) was then created as an encoding scheme for UTM coordinates to make them easier to communicate. After the War, UTM gradually gained users, especially in the scientific community. Because UTM zones do not align with political boundaries, several countries followed the United Kingdom in creating their own national or regional grid systems based on custom projections. The use and invention of such systems especially proliferated during

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3234-494: The central meridian. Therefore, meridians are equally spaced along a given parallel. On a pseudocylindrical map, any point further from the equator than some other point has a higher latitude than the other point, preserving north-south relationships. This trait is useful when illustrating phenomena that depend on latitude, such as climate. Examples of pseudocylindrical projections include: The HEALPix projection combines an equal-area cylindrical projection in equatorial regions with

3311-410: The church becomes 696017. This reference describes a 100-metre by 100-metre square, and not a single point, but this precision is usually sufficient for navigation purposes. The symbols on the map are not precise in any case, for example the church in the example above would be approximately 100x200 metres if the symbol was to scale, so in fact, the middle of the black square represents the map position of

3388-407: The cone intersects the globe—or, if the map maker chooses the same parallel twice, as the tangent line where the cone is tangent to the globe. The resulting conic map has low distortion in scale, shape, and area near those standard parallels. Distances along the parallels to the north of both standard parallels or to the south of both standard parallels are stretched; distances along parallels between

3465-553: The correspondence between a flat map and the round Earth is necessarily imperfect. At the South Pole , grid north conventionally points northwards along the Prime Meridian . Since the meridians converge at the poles, true east and west directions change rapidly in a condition similar to gimbal lock . Grid north solves this problem. Locations in a projected coordinate system, like any cartesian coordinate system, are measured and reported as easting/northing or ( x , y ) pairs. The pair

3542-586: The distortion in projections. Like Tissot's indicatrix, the Goldberg-Gott indicatrix is based on infinitesimals, and depicts flexion and skewness (bending and lopsidedness) distortions. Rather than the original (enlarged) infinitesimal circle as in Tissot's indicatrix, some visual methods project finite shapes that span a part of the map. For example, a small circle of fixed radius (e.g., 15 degrees angular radius ). Sometimes spherical triangles are used. In

3619-416: The equator 500km west of the central meridian of the zone (the edge of the zone itself is just under 400km to the west). This has the desirable effect of making all coordinates within the zone positive values, being east and north of the origin. Because of this, they are often referred to as the easting and northing . Grid north ( GN ) is a navigational term referring to the direction northwards along

3696-445: The equator and not a meridian. Pseudocylindrical projections represent the central meridian as a straight line segment. Other meridians are longer than the central meridian and bow outward, away from the central meridian. Pseudocylindrical projections map parallels as straight lines. Along parallels, each point from the surface is mapped at a distance from the central meridian that is proportional to its difference in longitude from

3773-458: The expense of others. Because the Earth's curved surface is not isometric to a plane, preservation of shapes inevitably requires a variable scale and, consequently, non-proportional presentation of areas. Similarly, an area-preserving projection can not be conformal , resulting in shapes and bearings distorted in most places of the map. Each projection preserves, compromises, or approximates basic metric properties in different ways. The purpose of

3850-410: The first half of the 20th century, projecting a human head onto different projections was common to show how distortion varies across one projection as compared to another. In dynamic media, shapes of familiar coastlines and boundaries can be dragged across an interactive map to show how the projection distorts sizes and shapes according to position on the map. Another way to visualize local distortion

3927-433: The geoid are used to project maps from. Other regular solids are sometimes used as generalizations for smaller bodies' geoidal equivalent. For example, Io is better modeled by triaxial ellipsoid or prolated spheroid with small eccentricities. Haumea 's shape is a Jacobi ellipsoid , with its major axis twice as long as its minor and with its middle axis one and half times as long as its minor. See map projection of

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4004-400: The globe and projecting its features onto a specified surface. Although most projections are not defined in this way, picturing the light source-globe model can be helpful in understanding the basic concept of a map projection. A surface that can be unfolded or unrolled into a plane or sheet without stretching, tearing or shrinking is called a developable surface . The cylinder , cone and

4081-429: The globe never preserves or optimizes metric properties, so that possibility is not discussed further here. Tangent and secant lines ( standard lines ) are represented undistorted. If these lines are a parallel of latitude, as in conical projections, it is called a standard parallel . The central meridian is the meridian to which the globe is rotated before projecting. The central meridian (usually written λ 0 ) and

4158-551: The grid lines of a map projection . It is contrasted with true north (the direction of the North Pole ) and magnetic north (the direction in which a compass needle points). Many topographic maps , including those of the United States Geological Survey and Great Britain's Ordnance Survey , indicate the difference between grid north, true north, and magnetic north. The grid lines on Ordnance Survey maps divide

4235-498: The land surface. Auxiliary latitudes are often employed in projecting the ellipsoid. A third model is the geoid , a more complex and accurate representation of Earth's shape coincident with what mean sea level would be if there were no winds, tides, or land. Compared to the best fitting ellipsoid, a geoidal model would change the characterization of important properties such as distance, conformality and equivalence . Therefore, in geoidal projections that preserve such properties,

4312-421: The latitude and longitude of the natural origin, the false northing and false easting, and an overall scale factor. Given the parameters associated with particular location or grin, the projection formulas for the transverse Mercator are a complex mix of algebraic and trigonometric functions. Every map projection has a natural origin , e.g., at which the ellipsoid and flat map surfaces coincide, at which point

4389-535: The location of the Spire of Dublin on O'Connell Street may be given as 315904, 234671 as well as O1590434671. Coordinates in this format must never be truncated, because, for example, 31590, 23467 is also a valid location. Grid reference When the first standardized coordinate systems were created during the 20th century, such as the Universal Transverse Mercator , State Plane Coordinate System , and British National Grid , they were commonly called grid systems ;

4466-466: The map determines which projection should form the base for the map. Because maps have many different purposes, a diversity of projections have been created to suit those purposes. Another consideration in the configuration of a projection is its compatibility with data sets to be used on the map. Data sets are geographic information; their collection depends on the chosen datum (model) of the Earth. Different datums assign slightly different coordinates to

4543-427: The mapped graticule would deviate from a mapped ellipsoid's graticule. Normally the geoid is not used as an Earth model for projections, however, because Earth's shape is very regular, with the undulation of the geoid amounting to less than 100 m from the ellipsoidal model out of the 6.3 million m Earth radius . For irregular planetary bodies such as asteroids , however, sometimes models analogous to

4620-416: The number of possible map projections. More generally, projections are considered in several fields of pure mathematics, including differential geometry , projective geometry , and manifolds . However, the term "map projection" refers specifically to a cartographic projection. Despite the name's literal meaning, projection is not limited to perspective projections, such as those resulting from casting

4697-403: The plane are all developable surfaces. The sphere and ellipsoid do not have developable surfaces, so any projection of them onto a plane will have to distort the image. (To compare, one cannot flatten an orange peel without tearing and warping it.) One way of describing a projection is first to project from the Earth's surface to a developable surface such as a cylinder or cone, and then to unroll

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4774-487: The printing of grids on maps by the U.S. Army Map Service (AMS) and other combatants. Initially, each theater of war was mapped in a custom projection with its own grid and coding system, but this resulted in confusion. This led to the development of the Universal Transverse Mercator coordinate system , possibly adopted from a system originally developed by the German Wehrmacht . To facilitate unambiguous reporting,

4851-409: The projection formulas generate a coordinate of (0,0). To ensure that the northing and easting coordinates on a map are not negative (thus making measurement, communication, and computation easier), map projections may set up a false origin , specified in terms of false northing and false easting values, that offset the true origin. For example, in UTM, the origin of each northern zone is a point on

4928-468: The projection surface into a flat map. The most common projection surfaces are cylindrical (e.g., Mercator ), conic (e.g., Albers ), and planar (e.g., stereographic ). Many mathematical projections, however, do not neatly fit into any of these three projection methods. Hence other peer categories have been described in the literature, such as pseudoconic, pseudocylindrical, pseudoazimuthal, retroazimuthal, and polyconic . Another way to classify projections

5005-447: The real church, independently of the actual size of the church. Grid references comprising larger numbers for greater precision could be determined using large-scale maps and an accurate Romer . This might be used in surveying but is not generally used for land navigating for walkers or cyclists, etc. The growing availability and decreasing cost of handheld GPS receivers enables determination of accurate grid references without needing

5082-438: The same location, so in large scale maps, such as those from national mapping systems, it is important to match the datum to the projection. The slight differences in coordinate assignation between different datums is not a concern for world maps or those of large regions, where such differences are reduced to imperceptibility. Carl Friedrich Gauss 's Theorema Egregium proved that a sphere's surface cannot be represented on

5159-440: The scale factor h along the meridian, the scale factor k along the parallel, and the angle θ ′ between them, Nicolas Tissot described how to construct an ellipse that illustrates the amount and orientation of the components of distortion. By spacing the ellipses regularly along the meridians and parallels, the network of indicatrices shows how distortion varies across the map. Many other ways have been described of showing

5236-824: The significant digits (3,4, and 5 in this case) are known to both parties. Alphanumeric encodings typically use codes to replace the most significant digits by partitioning the world up into large grid squares. For example, in the Military Grid Reference System , the above coordinate is in grid 11U (representing UTM Zone 11 5xxxxxx mN), and grid cell NS within that (representing the second digit 5xxxxxmE x6xxxxxm N), and as many remaining digits as are needed are reported, yielding an MGRS grid reference of 11U NS 949 361 (or 11U NS 9493 3617 or 11U NS 94934 36174). The Ordnance Survey National Grid (United Kingdom) and other national grid systems use similar approaches. In Ordnance Survey maps, each Easting and Northing grid line

5313-427: The sphere. In reality, cylinders and cones provide us with convenient descriptive terms, but little else. Lee's objection refers to the way the terms cylindrical , conic , and planar (azimuthal) have been abstracted in the field of map projections. If maps were projected as in light shining through a globe onto a developable surface, then the spacing of parallels would follow a very limited set of possibilities. Such

5390-423: The standard parallels are compressed. When a single standard parallel is used, distances along all other parallels are stretched. Conic projections that are commonly used are: Azimuthal projections have the property that directions from a central point are preserved and therefore great circles through the central point are represented by straight lines on the map. These projections also have radial symmetry in

5467-403: The surface into a plane. While the first step inevitably distorts some properties of the globe, the developable surface can then be unfolded without further distortion. Once a choice is made between projecting onto a cylinder, cone, or plane, the aspect of the shape must be specified. The aspect describes how the developable surface is placed relative to the globe: it may be normal (such that

5544-432: The surface's axis of symmetry coincides with the Earth's axis), transverse (at right angles to the Earth's axis) or oblique (any angle in between). The developable surface may also be either tangent or secant to the sphere or ellipsoid. Tangent means the surface touches but does not slice through the globe; secant means the surface does slice through the globe. Moving the developable surface away from contact with

5621-407: The term cylindrical as used in the field of map projections relaxes the last constraint entirely. Instead the parallels can be placed according to any algorithm the designer has decided suits the needs of the map. The famous Mercator projection is one in which the placement of parallels does not arise by projection; instead parallels are placed how they need to be in order to satisfy the property that

5698-632: The term is still common in some domains such as the military that encode coordinates as alphanumeric grid references . However, the term projected coordinate system has recently become predominant to clearly differentiate it from other types of spatial reference system . The term is used in international standards such as the EPSG and ISO 19111 (also published by the Open Geospatial Consortium as Abstract Specification 2), and in most geographic information system software. The map projection and

5775-422: The triaxial ellipsoid for further information. One way to classify map projections is based on the type of surface onto which the globe is projected. In this scheme, the projection process is described as placing a hypothetical projection surface the size of the desired study area in contact with part of the Earth, transferring features of the Earth's surface onto the projection surface, then unraveling and scaling

5852-464: The true central meridian at 117°W) and 5.6 million meters north of the equator . While such precise numbers are easy to store and calculate in GIS and other computer databases, they can be difficult for humans to remember and communicate. Thus, since the mid 20th century, there have been alternative encodings that shorten the numbers or convert the numbers into some form of alphanumeric string. For example,

5929-411: The whole Earth as a finite rectangle, except in the first two cases, where the rectangle stretches infinitely tall while retaining constant width. A transverse cylindrical projection is a cylindrical projection that in the tangent case uses a great circle along a meridian as contact line for the cylinder. See: transverse Mercator . An oblique cylindrical projection aligns with a great circle, but not

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