Super Output Areas -​ Middle Layer Digital Boundaries

Super Output Areas -​ Middle Layer Digital Boundaries

Middle Layer SOA Boundaries

Super Output Areas (SOAs) are a new geographic hierarchy designed to improve the reporting of small area statistics. They are already being introduced to Neighbourhood
Statistics and it is envisaged that they will eventually become a standard across National Statistics and beyond. England and Wales have three layers of SOA to support a range of disclosure requirements (Lower, Middle and Upper). Unlike wards, SOAs are of regular size and are not subject to regular boundary change. The layers are as follows:

Middle Layer SOAs are built from groups of contiguous Lower Layer SOAs and are constrained by the boundaries of local authorities (LAs) as at the end of 2002.

Note: Although not a true Middle Layer SOA (due to the population being too small), Isles of Scilly has been given a code in the Middle Layer SOA list in order to give complete coverage of the country for data matching. SOA Middle Layer statistics should not however be released for Isles of Scilly, only for the 7193 real Middle Layer SOAs.

• The 7193 Middle Layer SOAs (6780 in England, 413 in Wales) were generated via a two-​stage process:
o A draft set was generated by computer, in the same manner as the Lower Layer SOAs.
o Local authorities and other local agencies were invited to propose changes to the draft boundaries in order to establish SOAs that better met local needs. The consultation ran from March to May 2004 and led to publication of the final Middle Layer SOAs in August 2004.
• The minimum population of Middle Layer SOAs is 5000 and the mean 7200.
• Middle Layer SOAs however have names based on the statutory names of the LAs in which they are situated. The Middle Layer names are therefore of the form <LA name> xxx., where xxx represents a 3-​digit sequential number.

The first two years of SOA usage (up until 2006) are a trial period during which the use of SOAs will be reviewed and the need for boundary changes assessed. Thereafter, it is expected that SOAs will be fixed for a period of some length. A maintenance policy is also forthcoming to state how localised SOA amendments could be made if circumstances such as new housing estates or demolitions cause individual SOAs to move outside an acceptable size range.

The Middle Layer SOA boundaries are available on two CD-​ROMs, one containing MapInfo MID/​MIF format, the other containing Shapefile format. Both CD-​ROMs also contain a range of look-​up tables relating Output Areas, SOAs, ST wards and local authorities. Each CD-​ROM includes both high resolution (suitable for more detailed analytical work) mapped to the ’Extent of the Realm’, which is the statutory extent of the administrative areas on which SOAs are based (usually the Extent of the Realm (EOR) extends only as far as the Mean Low Water mark, but in some instances it extends out to sea to include offshore islands) and generalised boundaries (for quick and easy visualisation of the geography and for the creation of national and regional thematic maps of data for SOAs) constrained to the Mean High Water (MHW) mark, giving a more orthodox appearance to the coastline.

Note: these CD-​ROMs should not be used by Neighbourhood Statistics (NeSS) data suppliers to georeference their data. NeSS data suppliers should use the separate CD-​ROMs provided for this purpose.

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