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.