Irish grid reference system
The Irish grid reference system is a system of geographic grid references commonly used in Ireland (both Northern Ireland and the Republic of Ireland). The Irish grid overlaps the British grid.
Usage
In general, neither Ireland 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 co-ordinate system for Ireland called ITM, which will initially run in parallel with the existing Irish grid system.
Grid letters
The area of Ireland is divided into 20 squares, measuring 100km by 100km, each identified by a single letter.
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.
Summary parameters of the Irish Grid coordinate system:
- Datum: OSGB1936 Modified,
- 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
Examples
- O 008 741 (Newgrange Neolithic Tomb, Co Meath on OSNI 1:250000 mapping from OrdnanceSurvey.co.uk Get-a-Map).
- C 948 454 (Giant's Causeway, Co Antrim on OSNI 1:250000 mapping ibid).
External links
- History and overview of the system, from OSI
- OSI online grid converter. Registration required, but a made-up email address will suffice (Or enter: ie@ie.ie for the email address and password for the password.)
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