The Info List - Irish Grid Reference System

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The Irish grid reference system
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).[1] 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.


1 Usage 2 Grid letters 3 Eastings and northings 4 Summary parameters of the Irish Grid coordinate system 5 Notes 6 References 7 External links

Usage[edit] In general, neither Ireland
nor Great Britain
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
Ordnance Survey
of Ireland, the Ordnance Survey
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
Ordnance Survey
of Ireland
and the Ordnance Survey
Ordnance Survey
of Northern Ireland
jointly implemented a new coordinate system for Ireland
called Irish Transverse Mercator, or ITM, 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[citation needed] — a point in Lough Ree, close to the western (Co. Roscommon) shore, whose grid reference is N 000 500. This system is used for high accuracy professional digital mapping and surveying. Grid letters[edit]

Irish grid

The area of Ireland
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. Eastings and northings[edit] 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 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, the location of the Spire of Dublin
Spire of Dublin
on O'Connell Street
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. Summary parameters of the Irish Grid coordinate system[edit]

Spheroid: Airy Modified, Datum: 1965, Map projection: Transverse Mercator Latitude
of Origin: 53°30'00 N Longitude
of Origin: 8°00'00 W Scale Factor: 1.000 035 False Easting: 200000 m False Northing: 250000 m


^ How to Use Map Scales and Grids OSI


Leahy, Derek (September 26, 2008). "Irish Grid Reference System". Ordnance Survey
Ordnance Survey
Ireland : 185 years of innovation in mapping. Dublin: Ordnance Survey
Ordnance Survey
Ireland. Archived from the original on September 11, 2009. Retrieved 14 August 2009. 

External links[edit]

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 Iri