Getting a high response rate and quality representative data from those taking part in the Census is of upmost importance to the programme. ONS can only achieve this if they can identify each individual that they want to respond, locate their address and then send the Census documentation out to them in the post. For the 2001 Census, ONS used an address product that ended up being three-years out of date by the time the Census was conducted. For the 2011 Census, having learnt lessons from 2001, ONS recognised that the challenge was to produce an address register that was as current and up to date as possible in order to produce quality statistics.
To tackle this problem, ONS used comprehensive text matching algorithms to combine Royal Mail Postal Address File (PAF) with OS MasterMap Address Layer 2 (AL2), including pre-build content available from Ordnance Survey and the National Land and Property Gazetteer (NLPG) in order to create a comprehensive address register using the most up to date and accurate sources possible. To improve the quality of the content further, ONS conducted spatial building matching using OS MasterMap Topography Layer data; the most detailed topographic mapping data available from Ordnance Survey, to identify those addresses that actually matched with a building polygon on the topographic map. This cleansing process eliminated the majority of erroneous addresses created through misspellings and duplications. The output data was then shared with local authorities and Royal Mail so that ground surveys could be conducted for final verification purposes.
Any remaining un-matched addresses were verified by ONS using ground surveys.
- The collaborative working that Ordnance Survey and ONS developed for the 2011 Census influenced the creation of the AdressBase data product initiative, which now benefits all users seeking a definitive source of addressing.
- The creation of a centralised address register delivered value for money through the accurate delivery of postal questionnaires, which saved ONS an estimated £25 million in data collection costs.
- By using data products available from Ordnance Survey under the Public Sector Mapping Agreement (PSMA), ONS have been able to produce the most accurate address register to date, meeting address under coverage targets of within 1% and positional accuracy targets of 99%.
- Through the establishment of GeoPlace and the AddressBase initiative, ONS is no longer required to maintain a national address register, which has delivered a time and materials saving of around £8 million.
- Pre-build address content available within AL2 had provided intelligence on new build properties that was not available in any of the other address datasets.