Irish national grid reference system
Encyclopedia
The Irish grid reference system is a system of geographic grid reference
s commonly used in Ireland
(both Northern Ireland
and the Republic of Ireland
). The Irish grid overlaps the British grid
.
nor Great Britain
uses latitude
or longitude
in describing internal geographic locations. Instead grid reference
systems are in common usage.
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, 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.
The Ordnance Survey of Ireland has implemented a new coordinate system for Ireland called Irish Transverse Mercator
, or ITM, which will initially run 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 N 000 500.
Coordinates may also be given relative to the origin of the entire 500 by 500 km grid (in the format easting, northing). For example 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
Grid references define locations on maps using Cartesian coordinates. Grid lines on maps define the coordinate system, and are numbered to provide a unique reference to features....
s commonly used in Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
(both Northern Ireland
Northern Ireland
Northern Ireland is one of the four countries of the United Kingdom. Situated in the north-east of the island of Ireland, it shares a border with the Republic of Ireland to the south and west...
and the Republic of Ireland
Republic of Ireland
Ireland , described as the Republic of Ireland , is a sovereign state in Europe occupying approximately five-sixths of the island of the same name. Its capital is Dublin. Ireland, which had a population of 4.58 million in 2011, is a constitutional republic governed as a parliamentary democracy,...
). The Irish grid overlaps the British grid
British national grid reference system
The Ordnance Survey National Grid reference system is a system of geographic grid references used in Great Britain, different from using latitude and longitude....
.
Usage
In general, neither IrelandIreland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
nor Great Britain
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
uses latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
or longitude
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, minutes and seconds, and denoted by the Greek letter lambda ....
in describing internal geographic locations. Instead grid reference
Grid reference
Grid references define locations on maps using Cartesian coordinates. Grid lines on maps define the coordinate system, and are numbered to provide a unique reference to features....
systems are in common usage.
The national grid referencing system was devised by the Ordnance Survey
Ordnance Survey
Ordnance Survey , an executive agency and non-ministerial government department of the Government of the United Kingdom, is the national mapping agency for Great Britain, producing maps of Great Britain , and one of the world's largest producers of maps.The name reflects its creation together with...
, and is heavily used in their survey data, and in maps (whether published by the Ordnance Survey of Ireland, the Ordnance Survey of Northern Ireland
Ordnance Survey of Northern Ireland
Ordnance Survey of Northern Ireland was the official mapping agency of Northern Ireland. The agency ceased to exist separately on 1 April 2008 when it became part of Land and Property Services Northern Ireland, an executive agency of the Northern Ireland Department of Finance and Personnel, along...
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.
The Ordnance Survey of Ireland has implemented a new coordinate system for Ireland called Irish Transverse Mercator
Irish Transverse Mercator
Irish Transverse Mercator , is the geographic coordinate system for Ireland. It was implemented jointly by the Ordnance Survey Ireland and the Ordnance Survey of Northern Ireland in 2001...
, or ITM, which will initially run in parallel with the existing Irish grid system. In both systems, the true origin is at 53° 30' N, 8° W
8th meridian west
The meridian 8° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, the Atlantic Ocean, Europe, Africa, the Southern Ocean, and Antarctica to the South Pole.-Geography:...
— a point in Lough Ree
Lough Ree
Lough Ree is a lake in the midlands of Ireland, the second of the three major lakes on the River Shannon. Lough Ree is the second largest lake on the Shannon after Lough Derg. The other two major lakes are Lough Allen to the north, and Lough Derg to the south, there are also several minor lakes...
, close to the western (Co. Roscommon
County Roscommon
County Roscommon is a county in Ireland. It is located in the West Region and is also part of the province of Connacht. It is named after the town of Roscommon. Roscommon County Council is the local authority for the county...
) shore, whose grid reference is N 000 500.
Grid letters
The area of Ireland is divided into 25 squares, measuring 100 km by 100 km, each identified by a single letter. The squares are numbered A to Z with I being omitted. 7 of the squares do not actually cover any land in Ireland - A, E, K, P, U, Y and Z.Eastings and northings
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 east, 5 km north'. 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); the most common usage is the six figure grid reference, employing three digits in each coordinate to determine a 100 m square.Coordinates may also be given relative to the origin of the entire 500 by 500 km grid (in the format easting, northing). For example the location of the Spire of Dublin
Spire of Dublin
The Spire of Dublin, officially titled the Monument of Light is a large, stainless steel, pin-like monument in height, located on the site of the former Nelson's Pillar on O'Connell Street in Dublin, Ireland.-Details:...
on O'Connell Street
O'Connell Street
O'Connell Street is Dublin's main thoroughfare. It measures 49 m in width at its southern end, 46 m at the north, and is 500 m in length...
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.
Summary parameters of the Irish Grid coordinate system
- Datum: Airy Modified,
- Map projection: Transverse Mercator
- Latitude of Origin: 53°30'00 N
- Longitude of Origin: 8°00'00 W8th meridian westThe meridian 8° west of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, the Atlantic Ocean, Europe, Africa, the Southern Ocean, and Antarctica to the South Pole.-Geography:...
- Scale Factor: 1.000 035
- False Easting: 200000 m
- False Northing: 250000 m
Examples
- O 008 741 (NewgrangeNewgrangeNewgrange is a prehistoric monument located in County Meath, on the eastern side of Ireland, about one kilometre north of the River Boyne. It was built around 3200 BC , during the Neolithic period...
Neolithic tombNeolithic tombThe Neolithic tombs of Northwestern Europe, particularly Ireland, were built by the Neolithic people in the period 4000 - 2000 BC. There are four main types:* Passage graves* Portal dolmens* Court cairns* Wedge-shaped gallery graves...
, County MeathCounty MeathCounty Meath is a county in Ireland. It is part of the Mid-East Region and is also located in the province of Leinster. It is named after the ancient Kingdom of Mide . Meath County Council is the local authority for the county...
on OSNI 1:250000 mapping from OrdnanceSurvey.co.uk Get-a-Map). - C 948 454 (Giant's CausewayGiant's CausewayThe Giant's Causeway is an area of about 40,000 interlocking basalt columns, the result of an ancient volcanic eruption. It is located in County Antrim on the northeast coast of Northern Ireland, about three miles northeast of the town of Bushmills...
, County AntrimCounty AntrimCounty Antrim is one of six counties that form Northern Ireland, situated in the north-east of the island of Ireland. Adjoined to the north-east shore of Lough Neagh, the county covers an area of 2,844 km², with a population of approximately 616,000...
on OSNI 1:250000 mapping ibid).
External links
- The Irish Grid - A Description of the Co-ordinate Reference System used in Ireland -PDF (358kB) on the Irish Grid from OSi.
- PDF (221KB) detailing GPS to Irish Grid conversions
- A detailed (42-page) PDF file including history and map of the Irish grid and its links to Britain
- A two-page article for the American Society for Photogrammetry and Remote Sensing summarising the above.
- History and overview of the system, from OSI
- OSI online coordinate converter tool
- Clickable webmap that shows Irish grid references