Census Geography: Northern Ireland 2001

For the 2001 census in Northern Ireland a new census geography design method was adopted which created for the first time "Output Areas" (OAs) at the lowest level, specifically for the purpose of publishing census data. These were computer-generated and intended to be of uniform population size, take account of postcode and ward boundaries and to be as socially homogeneous as possible. The 5,022 Northern Ireland OAs contain an average of 336 persons and 125 households. The minimum threshold for publication of census data was 100 persons and 40 households and no OAs were created to be smaller than this. Digital boundaries were created for unit postcodes, and these were incorporated into the new OA boundaries.

OAs nest within local authority wards as of 31 December 2003, which was used as the reference date for the 2001 census geography. Some postcodes will be split across OA boundaries but OAs are an exact fit to wards. The local government tier comprises districts. There is no county level in the Northern Irish administrative geography and the characters 95 are used in this field which could contain a county code in England. The codes for these different levels are combined to create a 10-character alphanumeric code. Area names are applied to all levels about the OA. This census geography coding scheme will be found within postcode directories, census datasets and the Neighbourhood Statistics website.

A particular complexity with the 2001 census is that different population thresholds were set for different sets of statistical outputs. More detailed statistical tabulations known as the "standard tables" had thresholds of 1000 persons and 400 households and were intended to be available at the ward level. As some wards are less than the required size, there are unfortunately different versions of wards in a few instances, with the result that the census area statistics (CAS) ward and standard tables (ST) ward with the same area code may not refer to exactly the same geographical area!

In addition to the area-based hierarchy described here, 2001 census data for Northern Ireland were also published for regular grid squares, of 1km resolution in rural areas and 100m in urban areas. These require no digital boundaries and the data are freely available.

Digital boundary data are freely available for all units in the hierarchy.

Example