Super Output Areas (SOAs) are a geography designed for the collection and publication of small area statistics. They are used on the Neighbourhood Statistics site and across National Statistics.
There are currently two layers of SOA, with areas intermediate in size between census Output Areas (OAs) and local authorities and each layer nesting inside the layer above. This offers a choice of scale for the collection and publication of data, and allows for the release of local data that could be disclosive if published for OAs.
SOAs give an improved basis for comparison across the country because the units are more similar in size of population than, for example, electoral wards. They are also intended to be stable, enabling the improved comparison and monitoring of policy over time. In addition, figures for user defined geographies are aggregated and best fitted from data held for OAs and SOAs.
Lower Layer Super Output Areas -
The LSOAs were originally built using 2001 Census data from groups of Output Areas (typically four to six) and were constrained by the Standard Table wards used for 2001 Census outputs. They had a minimum size of 1,000 residents and 400 households, but average 1,500 residents. Measures of proximity (to give a reasonably compact shape) and social homogeneity (to encourage areas of similar social background) were also included.
(Note: the specific homogeneity criteria used related to type of dwelling - eg, detached/semi-detached etc. - and nature of tenure - eg, owner-occupied, private rented etc.).
Following the 2011 Census, there are now 34,753 Lower Layer SOAs (LSOAs) in England and Wales
Middle Layer Super Output Areas - There are now 7,201 Middle Layer SOAs (MSOAs) were defined in a two-stage process: an initial set was generated automatically but the boundaries were then modified in consultation with local authorities and other local bodies. The final boundaries were released to the public in August 2004.
- As with the LSOAs, initial Middle Layer SOAs were generated automatically by zone-design software. They were built using 2001 Census data from groups of Lower Layer SOAs and had a minimum size of 5,000 residents and 2,000 households. They also fitted within the boundaries of local authorities as at the end of 2002 (corresponding with the geography of the Census).
- A nationwide consultation exercise gave local authorities the opportunity to amend the initial Middle Layer SOAs to define areas more suited to local requirements. The consultation resulted in 7,193 MSOAs with an average population size of 7,200.
Changes to Output Areas following 2011 Census
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 (see 'Modification of output areas' below).
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.
Full details of changes to output area geographies as a result of the 2011 Census can be found here.