Local Government wards have a two-letter code within their local authority, and Census Output Areas an additional 4 digits within a ward. Census Output Areas (OAs) are the smallest unit for which census data is published - they contain at least 40 households (preferably 100), and are built up from postcode blocks after the census data is available, with a view to being socially as homogeneous as possible. A new set of Output Areas will be created for each decennial census. Census 2001 was the first to use this system - previously census data was published for larger Enumeration Districts which were delineated before the census was conducted. Enumeration Districts are still used for the collection of data but not for publication.
12UB
Cambridge district
12UBGA
Petersfield Ward
12UBGA0001
Output Area: Gwydir Street (north of junction with Hooper St)
An overlapping system encodes Civil Parish areas. Parishes are represented by an additional 3 digits within their local authority:
12UD
Fenland district
12UD010
Tydd St. Giles parish
Super Output Areas
Super Output Areas (SOAs) are a set of geographies developed after the 2001 census. The aim was to produce a set of areas of consistent size, whose boundaries would not change (unlike electoral wards). They are an aggregation of adjacent Output Areas with similar social characteristics. Lower Layer SOAs typically contain 4 to 6 OAs with a population of around 1500. Middle Layer SOAs on average have a population of 7,200. Upper Layer SOAs are still being calculated; they are expected to cover a population of at least 25,000 each.[1][2]
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