# Grid reference

Grid references define locations in maps using Cartesian coordinates. Grid lines on maps define the coordinate system, and are numbered to provide a unique reference to each location on the map. This reference is normally based on projected eastings and northings.

A typical map with grid lines

## Types

Grid systems vary, but the most common is a square grid with grid lines intersecting each other at right angles and numbered sequentially from the origin at the bottom left of the map. The grid numbers on the east-west (horizontal) axis are called Eastings, and the grid numbers on the north-south (vertical) axis are called Northings.

Numerical grid references consist of an even number of digits. Eastings are written before Northings. Thus in a 6 digit grid reference 123456, the Easting component is 123 and the Northing component is 456, i.e. if the smallest unit is 100 metres, it refers to a point 12.3 km east and 45.6 km north from the origin..

Grids may be arbitrary, or can be based on specific distances, for example some maps use a one-kilometre square grid spacing.

A grid reference locates a unique square region on the map. The precision of location varies, for example a simple town plan may use a simple grid system with single letters for Eastings and single numbers for Northings. A grid reference in this system, such as 'H3', locates a particular square rather than a single point.

Points can be located by grid references on maps that use a standard system for Eastings and Northings, such as the Universal Transverse Mercator used worldwide, or the Ordnance Survey National Grid used by Ordnance Survey in the UK. These points can then be located by someone else using grid references, even if using maps of a different scale.

In the Universal Transverse Mercator (UTM) system, grid reference is given by three numbers: zone, easting and northing. In the UTM system, the Earth is divided into 60 zones. Northing values are given by the metres north, or south (in the southern hemisphere) of the equator. Easting values are established as the distance from the central meridian of a zone. The central meridian is arbitrarily set at 500,000 metres, to avoid negative numbers. A position 100 kilometres west of a central meridian would have an easting of 400,000 metres. Due to its popularity, and worldwide cover, the UTM system is used worldwide by NATO as well as many countries, including Australia and the USA.[1]

In the United Kingdom, a proprietary grid system is used. In Ordnance Survey maps, each Easting and Northing grid line 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 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 below, 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 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 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 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 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 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, 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.

## References

1. ^
Caernarfonshire

Caernarfonshire (; Welsh: Sir Gaernarfon, Welsh pronunciation: [ˈsir gaɨ̯rˈnarvɔn]), historically spelled as Caernarvonshire or Carnarvonshire in English, is one of the thirteen historic counties, a vice-county and a former administrative county of Wales.

Claydon with Clattercot

Claydon with Clattercot is a civil parish in Oxfordshire, England. It was formed in 1932 by merger of the parish of Claydon (grid reference SP4550) with the extra-parochial area of Clattercote (grid reference SP4549). As at the United Kingdom Census 2011 its population was 306 and it had a total of 6.22km² of land, water and roads.

Cornbury and Wychwood

Cornbury and Wychwood is a civil parish in West Oxfordshire. It includes the country estate of Cornbury Park (Ordnance Survey grid reference SP350181) and the ancient former Royal Forest of Wychwood, which covers several square miles between Cornbury Park, the village of Leafield (grid reference SP3215) and the hamlet of Mount Skippett (SP352159).

Dartmoor

Dartmoor is an upland area in southern Devon, England. Protected by National Park status as Dartmoor National Park, it covers 954 km2 (368 sq mi).The granite which forms the uplands dates from the Carboniferous Period of geological history. The landscape consists of moorland capped with many exposed granite hilltops known as tors, providing habitats for Dartmoor wildlife. The highest point is High Willhays, 621 m (2,037 ft) above sea level. The entire area is rich in antiquities and archaeology.

Dartmoor is managed by the Dartmoor National Park Authority, whose 22 members are drawn from Devon County Council, local district councils and Government.

Parts of Dartmoor have been used as military firing ranges for over 200 years. The public is granted extensive land access rights on Dartmoor (including restricted access to the firing ranges) and it is a popular tourist destination.

Frankenbury Camp

Frankenbury Camp is the site of an Iron Age univallate hillfort located in Hampshire. The site is on a very slight promontory overlooking the Avon Valley on the north-western edge of the New Forest. The fort encloses approximately 11 acres. It has very steep natural slopes on the west and south sides. The northeast sides are defended by a simple rampart and ditch. The original entrance on the southeast corner has since been widened. It is listed as a scheduled ancient monument no.122. The site is currently pasture, and part of Folds Farm, for the most part, although the earthworks themselves are lined with trees and the south and western parts are now encroached by woodland. Various archaeological relics have been found in the area:

Iron Age/Roman Pottery:

At a permanent caravan site in an old gravel pit grid reference SU165142

Located east of caravan site in old gravel pit.grid reference SU165142

On farmland east of Criddlestyle grid reference SU161142.

Garden Cottage, Godshill. Located behind the cottage.grid reference SU174149

Located north west of Mews Hill Copsegrid reference SU165142Iron Age Coins

Durotrigian Silver Stater found in garden of Ambridge, Tinker's Cross, 1969.grid reference SU142158Roman Coins:

Found behind either Redlands or Garden Cottage, Godshill grid reference SU174149

Located in the garden of Avon Lodge. 1930. A coin of Constantine 306-337 A.D grid reference SU153141The artefacts are now in Salisbury Museum.

Irish grid reference system

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). The Irish grid partially overlaps the British grid, and uses a similar co-ordinate system but with a meridian more suited to its westerly location.

List of stone circles

A stone circle is a monument of stones arranged in a circle or ellipse. Such monuments have been constructed in many parts of the world throughout history for many different reasons. The best known tradition of stone circle construction occurred across the British Isles and Brittany in the Late Neolithic and Early Bronze Age, with over 1000 surviving examples, including Avebury, the Ring of Brodgar and Stonehenge. Another prehistoric tradition occurred in southern Scandinavia during the Iron Age, where stone circles were built to be mortuary monuments to the dead. Outside Europe, examples of stone circles include the 6300~6900 BCE Atlit Yam in Israel and 3000~4000 BCE Gilgal Refaim nearby, and the Bronze Age monuments in Hong Kong. Stone circles also exist in a megalithic tradition located in Senegal and the Gambia.This is an incomplete photographic list of these stone circles.

Midland Main Line

The Midland Main Line is a major railway line in England from London to Sheffield in the north of England. The line is under the Network Rail description of Route 19; it comprises the lines from London's St Pancras station via Leicester, Derby/Nottingham and Chesterfield in the East Midlands.

Express passenger services on the line are operated by East Midlands Trains. The section between St Pancras and Bedford is electrified and forms the northern half of Thameslink, with a semi-fast service to Brighton and other suburban services.

A northern part of the route, between Derby and Chesterfield, also forms part of the Cross Country Route operated by CrossCountry. Tracks from Nottingham to Leeds via Barnsley and Sheffield are shared with Northern. East Midlands Local also operates regional and local services using parts of the line.

Milecastle 50

Milecastle 50 (High House) was a milecastle on Hadrian's Wall (grid reference NY60676601).

Milecastle 53

Milecastle 53 (Banks Burn) was a milecastle on Hadrian's Wall (grid reference NY56486460).

Milecastle 63

Milecastle 63 (Walby West) was a milecastle on Hadrian's Wall (grid reference NY43155973).

Military Grid Reference System

The Military Grid Reference System (MGRS) is the geocoordinate standard used by NATO militaries for locating points on Earth. The MGRS is derived from the Universal Transverse Mercator (UTM) grid system and the Universal Polar Stereographic (UPS) grid system, but uses a different labeling convention. The MGRS is used for the entire Earth.

An example of an MGRS coordinate, or grid reference, would be 4QFJ12345678, which consists of three parts:

4Q (grid zone designator, GZD)

FJ (the 100,000-meter square identifier)

12345678 (numerical location; easting is 1234 and northing is 5678, in this case specifying a location with 10 m resolution)An MGRS grid reference is a point reference system. When the term 'grid square' is used, it can refer to a square with a side length of 10 km (6 mi), 1 km, 100 m (328 ft), 10 m or 1 m, depending on the precision of the coordinates provided. (In some cases, squares adjacent to a Grid Zone Junction (GZJ) are clipped, so polygon is a better descriptor of these areas.) The number of digits in the numerical location must be even: 0, 2, 4, 6, 8 or 10, depending on the desired precision. When changing precision levels, it is important to truncate rather than round the easting and northing values to ensure the more precise polygon will remain within the boundaries of the less precise polygon. Related to this is the primacy of the southwest corner of the polygon being the labeling point for an entire polygon. In instances where the polygon is not a square and has been clipped by a grid zone junction, the polygon keeps the label of the southwest corner as if it had not been clipped.

4Q .....................GZD only, precision level 6° × 8° (in most cases)

4QFJ ...................GZD and 100 km Grid Square ID, precision level 100 km

4QFJ 1 6 ...............precision level 10 km

4QFJ 12 67 .............precision level 1 km

4QFJ 123 678 ...........precision level 100 m

4QFJ 1234 6789 .........precision level 10 m

4QFJ 12345 67890 .......precision level 1 m

Newton Purcell with Shelswell

Newton Purcell with Shelswell is a civil parish in Oxfordshire, England. It was formed in 1932 by merger of the parishes of Newton Purcell (grid reference SP6230) and Shelswell (grid reference SP6030).

Operation Fayette Canyon

Operation Fayette Canyon was a security operation during the Vietnam War in Quảng Nam Province, that took place from 15 December 1968 to 28 February 1969.

Ordnance Survey National Grid

The Ordnance Survey National Grid reference system is a system of geographic grid references used in Great Britain, distinct from latitude and longitude. It is often called British National Grid (BNG).The Ordnance Survey (OS) devised the national grid reference system, and it is heavily used in their survey data, and in maps based on those surveys, whether published by 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 the Isle of Man); the Irish grid reference system was a similar system created by the Ordnance Survey of Ireland and the Ordnance Survey of Northern Ireland for the island of Ireland. The Universal Transverse Mercator coordinate system (UTM) is used to provide grid references for worldwide locations, and this is the system commonly used for the Channel Islands and Ireland (since 2001). European-wide agencies also use UTM when mapping locations, or may use the Military Grid Reference System (MGRS) system, or variants of it. OSGB uses Orthorectified images of many temporal resolution for one area.

River Ottery

The River Ottery (Cornish: Otri) is a small river in northeast Cornwall, United Kingdom. The river is about twenty miles (32 km) long from its source southeast of Otterham to its confluence with the River Tamar at Nether Bridge, two miles (3.2 km) northeast of Launceston.The headwaters of the River Ottery are within the civil parish of Otterham but formerly came under the parish of Forrabury and Minster. In 1311, the rector of that parish wrote: "..the river Ottery takes its rise in this parish and flows to Canworthy Water and so by Yeolmbridge to the river Tamar."

River Waldron

The River Waldron is a small river in Cheshire in north west England. It drains water from the area between Audley and Crewe, and joins the River Weaver to the east of Crewe (grid reference SJ664560). It is known by several different names among its length, including Alsager Brook and Valley Brook. Its principle tributaries are Wistaston Brook and Barthomley Brook.

It rises in Parrot's Drumble on the outskirts of Talke, and flows roughly westwards through Alsager and Crewe.

Savernake Forest

Savernake Forest stands on a Cretaceous chalk plateau between Marlborough and Great Bedwyn in Wiltshire, England. Its area is approximately 4,500 acres (18 km2; 7.0 sq mi).Most of the forest lies within the civil parish of Savernake. It is privately owned by the Earl of Cardigan and his son Viscount Savernake, and is administered by trustees. Since 1939 the timber of the forest has been managed by the Forestry Commission on a 999-year lease. The private status of Savernake, Britain's only privately owned forest, is maintained by shutting the forest to the public one day per year.

Spatial reference system

A spatial reference system (SRS) or coordinate reference system (CRS) is a coordinate-based local, regional or global system used to locate geographical entities. A spatial reference system defines a specific map projection, as well as transformations between different spatial reference systems. Spatial reference systems are defined by the OGC's Simple Feature Access using well-known text representation of coordinate reference systems, and support has been implemented by several standards-based geographic information systems. Spatial reference systems can be referred to using a SRID integer, including EPSG codes defined by the International Association of Oil and Gas Producers.

It is specified in ISO 19111:2007 Geographic information—Spatial referencing by coordinates, prepared by ISO/TC 211, also published as OGC Abstract Specification, Topic 2: Spatial referencing by coordinate.

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