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Census Geography: Northern Ireland 1991

The smallest areal units of the 1991 census geography hierarchy in Northern Ireland are "Enumeration Districts" (EDs). These areas were each the responsibility of a single census enumerator. Digitised boundaries for these EDs were created by Ordnance Survey (Northern Ireland). The 3,729 NI 1991 EDs contain an average of 414 persons and 142 households. The minimum threshold for publication of census data was 50 persons and 25 households and there were no "restricted EDs" of the type found elsewhere in the UK where populations fell below these thresholds. There is no clear relationship between ED and postcode geography because they were created by completely separate processes.

EDs nest within wards as of 21 April 1991, the date of the census. Wards have a mean size of 2,725 persons or 939 households. The local government tier comprises the 26 districts councils within Northern Ireland. The codes for these different levels are combined to create a 5-or 6-digit numeric code for each ED, with two digits for each of ward and ED. Area names are applied at the and ward levels, but EDs have only numbers.

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 available for all units in the hierarchy but registration is required.


Table 1: 1991 Census geography hierarchy within Northern Ireland

Areatype Code Full code Area name Number Mean population
District council 1 1 Antrim 26 59,312
Ward 01 1010 Aldergrove 568 2,725
Enumeration district 04 10104 (not named) 3,729 414