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56-564: Wandlebury Hill ( grid reference TL493534 ) is a peak in the Gog Magog Hills , a ridge of low chalk hills extending for several miles to the southeast of Cambridge , England. The underlying rock is present in a number of places on the hill. At 74 metres (243 ft) it is the same height as the nearby Little Trees Hill , although the latter is a more notable landmark. The top stands in Wandlebury Country Park,

112-556: A nature reserve owned by Cambridge Past, Present & Future (registered charity number 204122), formerly known as the Cambridge Preservation Society. Wandlebury was already inhabited in the Bronze Age and 2500 years ago there was an Iron Age hill fort here known as Wandlebury Ring . This hill fort once had concentric ditches and earthen walls which were kept in place by wooden palisades . Although

168-459: 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

224-529: A 100 m square. For example, the grid reference of the 100 m square containing the summit of Ben Nevis is NN 166 712 . (Grid references may be written with or without spaces; e.g., also NN166712.) NN has an easting of 200 km and northing of 700 km, so the OSGB36 National Grid location for Ben Nevis is at 216600, 771200. Grid references may also be quoted as a pair of numbers: eastings then northings in metres, measured from

280-465: 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

336-669: 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

392-415: 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

448-455: 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

504-554: 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,

560-499: A military grid. Four of these largest squares contain significant land area within Great Britain: S, T, N and H. The O square contains a tiny area of North Yorkshire , Beast Cliff at OV 0000 , almost all of which lies below mean high tide. For the second letter, each 500 km square is subdivided into 25 squares of size 100 km by 100 km, each with a letter code from A to Z (again omitting I) starting with A in

616-752: A point in the Atlantic Ocean well to the west of Great Britain. In Cornwall , the WGS 84 longitude lines are about 70 metres east of their OSGB 36 equivalents, this value rising gradually to about 120 m east on the east coast of East Anglia . The WGS 84 latitude lines are about 70 m south of the OSGB 36 lines in South Cornwall , the difference diminishing to zero in the Scottish Borders , and then increasing to about 50 m north on

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672-587: 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

728-527: Is a system of geographic grid references , distinct from latitude and longitude , whereby any location in Great Britain can be described in terms of its distance from the origin (0, 0), which lies to the west of the Isles of Scilly . The Ordnance Survey (OS) devised the national grid reference system, and it is heavily used in its survey data, and in maps based on those surveys, whether published by

784-461: Is applied. This creates two lines of longitude about 180 km east and west of the central meridian along which the local scale factor equals 1, i.e. map scale is correct. Inside these lines the local scale factor is less than 1, with a minimum of 0.04% too small at the central meridian. Outside these lines the local scale factor is greater than 1, and is about 0.04% too large near the east and west coasts. Grid north and true north are only aligned on

840-600: 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

896-569: Is published by the Ordnance Survey is called the National Grid Transformation OSTN15. This models the detailed distortions in the 1936–1962 retriangulation, and achieves backwards compatibility in grid coordinates to sub-metre accuracy. The difference between the coordinates on different datums varies from place to place. The longitude and latitude positions on OSGB 36 are the same as for WGS 84 at

952-436: 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

1008-620: Is the system commonly used for the Channel Islands . European-wide agencies also use UTM when mapping locations, or may use the Military Grid Reference System (MGRS), or variants of it. The first letter of the British National Grid is derived from a larger set of 25 squares of size 500 km by 500 km, labelled A to Z, omitting one letter (I) (refer diagram below), previously used as

1064-597: 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

1120-692: The English Channel halfway between Dover and Calais , the ED50 longitude lines are about 20 m east of the OSGB36 equivalents, and the ED50 latitude lines are about 150 m south of the OSGB36 ones. 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 ;

1176-628: The English Channel which lies between the island of Jersey and the French port of St. Malo ). Over the Airy ellipsoid a straight line grid, the National Grid, is placed with a new false origin to eliminate negative numbers, creating a 700 km by 1300 km grid. This false origin is located south-west of the Isles of Scilly. In order to minimize the overall scale error, a factor of 2499/2500

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1232-660: 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

1288-602: The Isle of Man ). The Irish grid reference system is a similar system created by the Ordnance Survey of Ireland and the Ordnance Survey of Northern Ireland for the island of Ireland. The Irish Transverse Mercator (ITM) coordinate reference system was adopted in 2001 and is now the preferred coordinate reference system across Ireland. ITM is based on the Universal Transverse Mercator coordinate system (UTM), used to provide grid references for worldwide locations, and this

1344-504: 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

1400-628: 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

1456-434: 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

1512-465: The Ordnance Survey or by commercial map producers. Grid references are also commonly quoted in other publications and data sources, such as guide books and government planning documents. A number of different systems exist that can provide grid references for locations within the British Isles : this article describes the system created solely for Great Britain and its outlying islands (including

1568-552: The Ring. The house was demolished in the 1950s but the monumental stable block remains, now used for accommodation and as headquarters office of Cambridge Past, Present & Future. The grave of the Godolphin Barb horse, which died in 1753, can be seen under the archway. Maps and leaflets are available from the porch at all times and from a shed in car park on summer Sundays. The tail of a crashed World War II Wellington Bomber

1624-547: 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

1680-608: 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

1736-525: The central meridian (400 km easting) of the grid which is 2° W (OSGB36) and approx. 2° 0′ 5″ W ( WGS 84 ). A geodetic transformation between OSGB 36 and other terrestrial reference systems (like ITRF2000 , ETRS89 , or WGS 84 ) can become quite tedious if attempted manually. The most common transformation is called the Helmert datum transformation , which results in a typical 7 m error from true. The definitive transformation from ETRS89 that

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1792-410: 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

1848-559: 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

1904-416: 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

1960-532: The fort has vanished, the ditch (the Ring) dug around the edge can clearly be seen and walked along, being 5 metres deep in places and offering an adventurous route along its edge. There is no evidence that it was ever used in defence. The reserve, mainly beech woodlands and fields, is a place for birdwatching . Banyard bird hide, overlooking Varley's Field, was completed in February 2012. Like Little Trees Hill,

2016-570: 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

2072-421: 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

2128-453: The north coast of Scotland . (If the lines are further east , then the longitude value of any given point is further west . Similarly, if the lines are further south, the values will give the point a more northerly latitude.) The smallest datum shift is on the west coast of Scotland and the greatest in Kent . These two datums are not both in general use in any one place, but for a point in

2184-429: The north-west corner to Z in the south-east corner. These squares are outlined in light grey on the "100km squares" map, with those containing land lettered. The central (2° W) meridian is shown in red. Within each square, eastings and northings from the south west corner of the square are given numerically. For example, NH0325 means a 1 km square whose south-west corner is 3 km east and 25 km north from

2240-495: 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,

2296-409: 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

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2352-447: 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

2408-752: 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

2464-427: The south-west corner of square NH. A location can be indicated to varying resolutions numerically, usually from two digits in each coordinate (for a 1 km square) through to five (for a 1 m square); in each case the first half of the digits is for the first coordinate and the second half for the other. The most common usage is the six figure grid reference , employing three digits in each coordinate to determine

2520-405: The south-west to NN400900 in the north-east) the abbreviated grid reference 166712 is equivalent to NN166712. If working with more than one Landranger sheet, this may also be given as 41/166712. Alternatively, sometimes numbers instead of the two-letter combinations are used for the 100×100 km squares. The numbering follows a grid index where the tens denote the progress from West to East and

2576-554: The southwest corner of the SV square. 13 digits may be required for locations in Orkney and further north. For example, the grid reference for Sullom Voe Oil Terminal in the Shetland islands may be given as HU396753 or 439668,1175316 . Another, distinct, form of all-numeric grid reference is an abbreviated alphanumeric reference where the letters are simply omitted, e.g. 166712 for

2632-722: The standard projection for Ordnance Survey maps. The Airy ellipsoid is a regional best fit for Britain; more modern mapping tends to use the GRS80 ellipsoid used by the Global Positioning System (the Airy ellipsoid assumes the Earth to be about 1 km smaller in diameter than the GRS80 ellipsoid, and to be slightly less flattened). The British maps adopt a transverse Mercator projection with an origin (the "true" origin) at 49° N , 2° W (an offshore point in

2688-415: The summit is on public land and is accessible when sheep or Highland cattle are not in the field. Dogs must be on a lead everywhere in Wandlebury Country Park. It can be reached by walking across the field from post 3 of the nature trail. Virtually no climb is involved in the ascent, just a stroll through woodland. Wandlebury House, home of among others Francis Godolphin, 2nd Earl of Godolphin , stood within

2744-470: The summit of Ben Nevis. Unlike the numeric references described above, this abbreviated grid reference is incomplete; it gives the location relative to an OS 100×100 km square, but does not specify which square. It is often used informally when the context identifies the OS 2-letter square. For example, within the context of a location known to be on OS Landranger sheet 41 (which extends from NN000500 in

2800-647: 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

2856-467: 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,

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2912-588: The units from South to North. In the north of Scotland, the numbering is modified: the 100 km square to the north of 39 is numbered N30; the square to the north of 49 is N40, etc. The grid is based on the OSGB36 datum (Ordnance Survey Great Britain 1936, based on the Airy 1830 ellipsoid ), and was introduced after the retriangulation of 1936–1962 . It replaced the Cassini Grid which had previously been

2968-533: Was able to draw out the pattern of what he claimed were 3 hill figures picturing ancient British deities - A horse goddess ( Magog or Epona ), a Sun god ( Gog , Bel , Belinus or Lucifer ) and a warrior figure with sword and shield. The Times reported on Lethbridge's discovery as a "previously lost, three thousand-year-old hill-figure". A later article about Lethbridge's efforts was written by W. A. Clark in 1997 which did not confirm his claims, nor did magnetometer and resistivity meter testing. The suggestion

3024-474: Was dismissed by Glyn Daniel who commented that Lethbridge had not found any real antiquities but was "probably confusing geological features". A report by the Council for British Archaeology concluded that the 'hollows' were caused by common geological processes. Ordnance Survey National Grid The Ordnance Survey National Grid reference system ( OSGB ), also known as British National Grid ( BNG ),

3080-475: Was thought to have been overgrown or effaced in the 18th century. The figure was first recorded by Bishop Joseph Hall in 1605 and later by others including William Cole and John Layer. Investigation was carried out in 1954 by T. C. Lethbridge , an archaeologist and parapsychologist . He found small lumps of chalk to the south of the hill and proceeded to survey the area with a sounding bar, probing areas of soft ground and disturbed chalk. By placing markers he

3136-473: Was visible wedged high in a beech tree within the estate, until it was dislodged by strong winds in the early 1990s. A number of hypotheses have been made about a supposed "Wandlebury enigma"; the purpose, function and decoration of Wandlebury Hill. The first is the suggestion that an ancient hill figure had once been carved into the side of Wandlebury Hill, similar to the Cerne Abbas Giant . This

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