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Census Geography: England 2001

For the 2001 census in England 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, to take account of postcode and ward boundaries and to be as socially homogeneous as possible. The 165,665 English OAs contain an average of 297 persons and 124 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. Because no definitive boundaries exist for unit postcodes, these were automatically generated as part of the OA design process and the OA boundaries can therefore contain large "spikes" and other irregularities reflecting the computer-generated nature of the underlying postcode 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. Wards vary widely in population size, but tend to be of similar population sizes within a single local government area. The local government tier comprises local authority districts, London Boroughs and unitary authorities. In those parts of the country with a two-tier local government structure (typically counties and districts), the district level nests within the county level and this is reflected in the coding of the census areas. 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. Where there is only one tier of local government (unitary authorities), there is no county code and the characters 00 are used in this field. 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 used 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!

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


Table 1: 2001 Census geography hierarchy within English two-tier local government

Areatype Code Full code Area name Number Mean population
County 24 24 Hampshire 42 975,311
District UN 24UN Test Valley 308 132,997
Ward GF 24UNGF Blackwater 7,969 6,166
Enumeration district 0010 24UNGF0010 (Not named) 165,665 297

Table 2: 2001 Census geography hierarchy within English unitary authority

Areatype Code Full code Area name Number Mean population
County 00 00 (No county)    
District MS 00MSNC0020 Southampton 46 177,734
Ward NC 00MSNC0020 Portswood 7,969 6,166
Enumeration district 0020 00MSNC0020 (Not named) 165,665 297