I'm wondering which co-ordinate reference system would be the best to use for a project covering the British Isles, since the UK and Ireland have separate systems - British National Grid and Irish National Grid /Irish Transverse Mercator.

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    Opendata Postcodes (Codepoint) has the same issue with Northern Ireland data [BT Postcodes] (is in Irish National Grid) would project Irish National Grid to OSGB36 National Grid see old post blog.da.vidnicholson.com/2006/12/uk-postcode-coverage-map.html
    – Mapperz
    Jun 30, 2015 at 14:57
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    What is the source of your data. OSGB (Transverse Mercator), as you correctly point out, has SRID of 27700. The Irish National Grid uses same projection, and the same reference ellipsoid (Airy), but a different datum, false eastings, etc. I believe it is reasonably straightforward to convert from one to the other, seeing as they use the same underlying projections and ellipsoid. So, I would stick with 27700/29902, as this is the best fit for British Isles. Jun 30, 2015 at 16:48
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    Seeing as they are not contiguous, I would think you could keep using separate SRIDs for Ireland plus rest of UK. However, you haven't really stated what you project goals are, so maybe one of the UTM zones or an ETRS89 projection might be better. Jun 30, 2015 at 16:53
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    Depends what you are trying to do and what system you are using. In my job i deal with ROI, NI and GB. I use Irish Grid for the island of Ireland and OSGB for England, Scotland and Wales. In most the likes of QGIS, it allows for the reprojection of the layer to match the project CRS.
    – Ger
    Jul 2, 2015 at 11:55

2 Answers 2


I'd use something like EPSG:3035 - it's a reasonable European projection that is equal area so it's suitable for most statistical mapping.


You need to look at the extent of each projection around this area. For Example: Double click in Layer (Inside Table of contents in ARCGIS) go to Coordinate System tab. And then you need to define whether it will be Projected or Geographic. Next, you need to analyse the features to compare with original extent, such as:







Linear Unit.

It will be helpful to you make a decision in further situation!

Let me know if you have any questions!

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    How does this answer the question? He is asking about appropriate CRS for British Isles, not how to find such a thing in ArcGIS. Jun 30, 2015 at 16:48

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