ONS coding system
ONS codes are geocodes maintained by the United Kingdom's Office for National Statistics to represent a wide range of geographical areas of the UK, for use in tabulating census and other statistical data. These codes are also known as GSS codes, where GSS refers to the "Government Statistical Service" of which ONS is part. The previous hierarchical system of codes was replaced as from January 2011 by a nine-character code for all types of geography, in which there is no relation between the code for a lower-tier area and the corresponding parent area. The  older coding system has now been phased out. Geography of the UK Census. Information from the 2011 Census is published for a wide variety of geographical units. These areas include: Neighbourhood Statistics Geography. Super Output Areas (SOAs) are a set of geographical areas developed following the 2001 census, initially to facilitate the calculation of the Indices of Deprivation 2004 and subsequently for a range of additional Neighbourhood Statistics (NeSS). The aim was to produce a set of areas of consistent size, whose boundaries would not change (unlike electoral wards), suitable for the publication of data such as the Indices of  Deprivation. They are an aggregation of adjacent Output Areas with similar social characteristics. Lower Layer Super Output Areas (LSOAs) typically contain 4 to 6 OAs with a population of around 1500. Middle Layer Super Output Areas (MSOAs) on average have a population of 7,200. The hierarchy of Output Areas and the two tiers of Super Output Areas have become known as the Neighbourhood Statistics Geography. MSOAs use the name of the local or unitary authority followed by three digits, for example "Tower Hamlets 022" which is codice_1. LSOAs use the name of the containing MSOA followed by a letter, for  example "Tower Hamlets 022C" which is codice_2. Former hierarchical coding system. The older ONS code was constructed top down: For example, codice_3 for Cambridgeshire. For example, codice_4 for Cambridge district or codice_5 for Fenland. For example, codice_6 for Greenwich (London Borough) or codice_7 for Middlesbrough. For example, codice_8 for Petersfield Ward within Cambridge district. Current GSS coding system. The current system replaces these codes with a fixed length code of nine characters. The first three characters indicate the level of geography and the six digits following define the individual unit. For example, the Royal Borough of Greenwich is coded as  codice_12, Middlesbrough is codice_13, Cambridge codice_14 and Fenland codice_15. The meaning of some common three character prefixes is as follows: In 2019, the House of Commons Library proposed names instead of numeric codes for MSOAs to make them easier to use. Nine-character GSS codes. A full and up-to-date listing of GSS names and codes may be found by following the link to ONS Geography's Code History Database, below.