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Boundary File Dataset Guidance

The following guidance notes are supplied to assist customers in making informed decisions about the various types of boundary file datasets available and their suitability for use.

Resolution:  The majority of boundary sets are available as Ungeneralised or Generalised (20m/50m/100m). 

Ungeneralised: These boundary file datasets are the highest resolution data available (usually meaning large file sizes). Use 'Ungeneralised' datasets for advanced GIS analysis (such as point-in-polygon allocation).

Generalised : Generalised boundary file datasets are designed for high quality mapping, preserving much of the original detail from the full dataset, but typically 10% of the file size. They are great when used in conjunction with the raster products and for producing detailed regional and local maps, or large wall maps. They are also suitable for non-demanding GIS analyses (such as buffering). Generalised boundary file datasets are a good compromise between detail and small file size.

What boundary dataset should I use?

Ungeneralised boundary file datasets are the most detailed representation of actual boundaries. They produce the most accurate allocations of point data to a required geography. Generalised boundary file datasets have been simplified. With less detail they are prepared for use in data visualisation and the publication of maps where the need for detail is not usually as great.

A Generalised (20M) boundary is within 20 metres of the Ungeneralised boundary.



Ireland is divided into four provinces - Leinster, Ulster, Munster and Connacht. Although they presently do not have any administrative functions, they are relevant for a number of historical, cultural and sporting reasons. The borders of the provinces coincide exactly with the boundaries of the administrative counties. Three of the nine counties in Ulster are within the jurisdiction of the State.

NUTS 3 regions

The Nomenclature of Territorial Units for Statistics (NUTS) was drawn up by Eurostat in order to define territorial units for the production of regional statistics across the European Union. The NUTS classification has been used in EU legislation since 1988, but it was only in 2003 that the EU Member States, the European Parliament and the Commission established the NUTS regions within a legal framework (Regulation (EC) No 1059/2003). The NUTS 3 boundaries were amended on 21st of November 2016 (Regulation (EC) No 2066/2016). The changes resulting from the amendment are that Louth has moved from the Border to the Mid-East and what was formerly South Tipperary has moved from the South-East to the Mid-West.

The regional authorities and the two regional assemblies were abolished in the Local Government Act 2014 and were replaced with three regional assemblies. The three regional assemblies are groupings of the new NUTS 3 boundaries.

Administrative counties

In census reports the country is divided into 31 administrative counties/cities. The Local Government Reform Act 2014 Section 9 provided for the amalgamation of the city and county councils in Limerick and Waterford, and North Tipperary and South Tipperary County Councils.

There are now 26 administrative counties including the five administrative counties of Cork County, Galway County, Dún Laoghaire-Rathdown, Fingal and South Dublin. There are 5 city/city and county areas namely Cork City, Limerick City and County, Waterford City and County, Dublin City and Galway City.

Electoral Divisions

There are 3,440 Electoral Divisions (EDs) which are the smallest legally defined administrative areas in the State. One ED, St. Mary's, straddles the Louth-Meath county border, and is presented in two parts in the SAPS tables, with one part in Louth and the other in Meath. There are 32 EDs with low population, which for reasons of confidentiality have been amalgamated into neighbouring EDs giving a total of 3,409 EDs which appear in the SAPS tables.

Small Areas

Small Areas are areas of population generally comprising between 80 and 120 dwellings created by The National Institute of Regional and Spatial Analysis (NIRSA) on behalf of the Ordnance Survey Ireland (OSi) in consultation with CSO. Small Areas were designed as the lowest level of geography for the compilation of statistics in line with data protection and generally comprise either complete or part of townlands or neighbourhoods. There is a constraint on Small Areas that they must nest within Electoral Division boundaries.

Small areas were used as the basis for the Enumeration in Census 2016. Enumerators were assigned a number of adjacent Small Areas constituting around 400 dwellings in which they had to visit every dwelling and deliver and collect a completed census form and record the dwelling status of unoccupied dwellings.

The small area boundaries have been amended in line with population data from Census 2016.

2013 Constituency boundaries

For the purpose of elections to Dáil Éireann, the country is divided into Constituencies which, under Article 16.4 of the Constitution of Ireland, have to be revised at least once every twelve years with due regard to changes in the distribution of the population. The Constituencies were last revised in 2013 and the Schedule to the Electoral (Amendment)(No 7) Act 2013 contains details of their composition.

Municipal Districts

There are 95 municipal districts covering the entire area of each county (apart from Dublin, Cork and Galway cities). Districts correspond with local electoral areas except in the case of the Dundalk, Kilkenny City, and Mullingar municipal districts, where each municipal district comprises two local electoral areas, and the metropolitan districts of Limerick and Waterford, which contain three local electoral areas each.

2014 Local Electoral Areas

Each county, city and city and county is divided into local electoral areas and members of local authorities are elected in these.  Local electoral areas and the number of members to be elected in each are specified in a statutory instrument for each local authority area.  These were most recently made in 2014 for all except Cork City, which was made in 2008.In general, LEAs are formed by aggregating Electoral Divisions.  However, in a number of cases Electoral Divisions are divided between LEAs to facilitate electors. 

Gaeltacht Areas

The Gaeltacht Areas Orders, 1956, 1967, 1974 and 1982 defined the Gaeltacht as comprising 155 Electoral Divisions or parts of Electoral Divisions in the counties of Cork, Donegal, Galway, Kerry, Mayo, Meath and Waterford. 

Na Limistéir Pleanála Teanga Ghaeltachta

The Gaeltacht Act 2012 gives statutory effect to the implementation of the 20-Year Strategy for the Irish Language 2010–2030. Under the act, Gaeltacht areas, as they currently stand, will be redesignated as Gaeltacht Language Planning Areas.

Settlements (Census towns, cities and suburbs)

Historically, for the censuses of 1926 to 1951, a census town was defined simply as a cluster of twenty or more houses and the precise delimitation of the town was left to the discretion of the individual enumerator concerned. As part of the general review of towns for the 1956 Census, the boundaries for the census towns were drawn up in consultation with the various Local Authorities applying uniform principles in all areas of the country. The definition of a census town was changed at the 1956 Census, from twenty houses to twenty occupied houses; this definition was also applied at the 1961 and 1966 Censuses.

From 1971 to 2006, Census towns were defined as a cluster of fifty or more occupied dwellings where, within a radius of 800 metres there was a nucleus of thirty occupied dwellings (on both sides of a road, or twenty on one side of a road), along with a clearly defined urban centre e.g. a shop, a school, a place of worship or a community centre. Census town boundaries were extended over time where there was an occupied dwelling within 200 metres of the existing boundary.

To avoid the agglomeration of adjacent towns caused by the inclusion of low density one off dwellings on the approach routes to towns the 2011 criteria were tightened, in line with UN criteria.

In Census 2016, a new Census town was defined as there being a minimum of 50 occupied dwellings, with a maximum distance between any dwelling and the building closest to it, of 100 metres, and where there was evidence of an urban centre (shop, school etc). The proximity criteria for extending existing 2006 Census town boundaries was also amended to include all occupied dwellings within 100 metres of an existing building. Other information based on OSi mapping and orthogonal photography was also taken into account when extending boundaries. Boundary extensions were generally made to include the land parcel on which a dwelling was built or using other physical features such as roads, paths etc.

Census towns which previously combined legal towns and their environs have been newly defined using the standard census town criteria (with the 100 metres proximity rule). For some towns the impact of this has been to lose area and population, compared with previous computations.

26 new census towns were created for the 2016 Census.