Super Output Areas are a geography 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, Lower Layer Super Output Area (LSOA) and Middle Layer Super Output Area (MSOA). The SOA layers form a hierarchy based on aggregations of Output Areas (OAs).
The two layers of SOA, with areas intermediate in size between census Output Areas (OAs) and local authorities, 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
Lower Layer SOAs were first built using 2001 Census data from groups of Output Areas (typically four to six) and have been updated following the 2011 Census. They have an average of roughly 1,500 residents and 650 households. Measures of proximity (to give a reasonably compact shape) and social homogeneity (to encourage areas of similar social background) are 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.).
1.09% of LSOAs were changed following the 2011 Census in order to maintain the characteristics described above. There are now 34,753 LSOAs in England and Wales.
Middle Layer Super Output Areas
As with the Lower Layer, Middle Layer SOAs are generated automatically by zone-design software using census data from groups of LSOAs. They have a minimum size of 5,000 residents and 3,000 households with an average population size of 7,500. They fit within local authority boundaries.
Following the 2011 Census 0.11% of MSOAs were changed in order to maintain minimum and average population criteria. There are now 7,201 MSOAs in England and Wales.
Following a public consultation in 2010 there is no firm demand for Upper Layer SOAs to be created for England.
SOA codes have 9 characters, generated as follows:
Example code: E01011949
|E||Letter to indicate country (E=England, W=Wales)|
|01||2 digit number indicates the SOA layer:
01 = Lower Layer
02 = Middle Layer
|000001||unique 6 digit tag for each zone (all SOA layers)|
Both Lower and Middle Layer SOA codes are grouped by local authority (LA) in the standard order of LA codes (i.e. starting with 00AA City of London). Lower Layer SOA codes do not have a geographic order within each LA, but Middle Layer SOA codes are applied on a north-south basis.
Scottish data zones have a similar 9-digit code of the form S01000001.
The coding scheme for Northern Irish SOAs does not follow this structure. Instead, they have an 8 character code, the first 6 digits relating to the ward code that each SOA nests within.