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Output Areas

Wondering what an Output Area is? This is what the Office of National Statistics has to say about them:

Output areas (OA) are created for Census data, specifically for the output of census estimates. The OA is the lowest geographical level at which census estimates are provided. Output areas were introduced in Scotland at the 1981 Census and in all the countries of the UK at the 2001 Census.

2001 Census OAs were built from clusters of adjacent unit postcodes but as they reflected the characteristics of the actual census data they could not be generated until after data processing. They were designed to have similar population sizes and be as socially homogenous as possible based on tenure of household and dwelling type (homogeneity was not used as a factor in Scotland).

Urban/rural mixes were avoided where possible; OAs preferably consisted entirely of urban postcodes or entirely of rural postcodes.

They had approximately regular shapes and tended to be constrained by obvious boundaries such as major roads.

The OAs were required to have a specified minimum size to ensure the confidentiality of data.

The minimum OA size was 40 resident households and 100 resident people but the recommended size was rather larger at 125 households. These size thresholds meant that unusually small wards and parishes were incorporated into larger OAs.

Maintaining stability as far as possible was key for the 2011 Census. Some modification of the previous Output Areas and Super Output Areas has taken place where a significant need has occurred since 2001.

The total of 2011 OAs is 171,372 for England and 10,036 for Wales. There are now 181,408 OAs, 34,753 LSOAs and 7,201 MSOAs in England and Wales. This means that 2.6 per cent of 2001 OAs have been changed as a result of the 2011 Census, along with 2.5 per cent of LSOAs and 2.1 per cent of MSOAs.

Significant points of interest for the 2011 Census are that output areas and super output areas align to local authority boundaries, including those that changed between 2003 and 2011, and also align at the border between Scotland and England. 161 OAs and SOAs were modified because they were considered unsuitable for reporting statistics. The average population in an OA has increased from 297 in 2001 to 309 in 2011.

Adapted from http://www.ons.gov.uk/ons/guide-method/geography/beginner-s-guide/census/output-area--oas-/index.html.

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