Output area production

The system for creating Output Areas was fully automated, and applied systematic and consistent criteria throughout the England and Wales. Its development became possible through the availability of increased computing power for automatic zoning methods, and also through the availability of co-ordinate referenced and postcoded data based on the Ordnance Survey Address Point product.

In simple terms, the system created Output Areas with around 125 households and populations which tended towards homogeneity. The 175,000 Output Areas 'nest' within wards and parishes, and normally comprise of whole unit postcodes as they were around the time of the Census. The system produced completely shaped areas following natural boundaries where possible, but the underlying patterns of streets and postcodes may result in convoluted shapes.

The system created a notional, computer held boundary around every address with no gaps between - a process known as 'tessellation'. The boundaries internal to each postcode unit (such as PO15 5RR) were removed, leaving a computer held boundary for each postcode. The system then looked for postcodes in contiguous clusters within each ward which optimised the mandatory and desirable criteria for Output Areas, using a process of very rapid iterative combinations. A map illustrating the various components is avilable to download from the link above, and the website prepared in 2001 by Professor David Martin of the University of Southampton provides a detailed account of the methods to be used in the Output Area production system was created.

Output Areas nest within the ward and parish/Community boundaries legally in force at the end of 2002. This includes ward boundaries operative in a number of local authorities in May 2003, and in some others in May 2004, a list of which is available as an Excel file. The adoption of boundaries current at the release date of the statistics was a requirement widely supported in consultation, and also complied with a wider National Statistics policy on harmonisation of boundaries.