Guidance

Changes to DWP statistical geographies in National and Official statistics

Updated 17 October 2025

Background

Unless specified, census-based geographies currently available for Official Statistics are derived from Census Output Areas (COAs). Development work and testing is underway to update our statistics to report on latest 2021 COA geographies. This is on a rolling basis starting from September 2025 and through into 2026. We will also take the opportunity to standardise the range of COA21 derived geographies available to users across different Official Statistics.  

Users will be informed of updates via the DWP Statistical Work Programme.

How Census Output Areas are allocated

COA’s are allocated using address information from the DWP Customer Information System (CIS). This is the most reliable source of addresses as it links to all of the DWP benefit systems and contains the most up-to-date address for each individual. 

The addresses are then put through a data cleansing procedure which ensures postcodes are formatted correctly and the address fields are populated correctly. 

2021 COAs are then assigned to claimants in this dataset using the ONS Postcode Directory, starting with a direct postcode to COA lookup and then working through a logical allocation routine. This dataset is referred to as the CIS Address History Database. These COAs are then used to merge on higher level geographies from the National Statistics Postcode Look-Up (NSPL).  

The CIS Address History database is mapped to statistical datasets to ensure that data extract dates fall between the address start and end of spell dates. If no known address can be matched for a period of time, a previous known address for that individual is used. This is more accurate than random allocation.

Effects of changing to 2021 Census Output Areas

For updates to OAs, LSOAs or MSOAs using Census 2021 data, ONS adhered to the same maximum limit of 5% change that was implemented in 2011 following public consultation. There were only 3 scenarios in which changes were made.

Change in the Output Area, Lower layer Super Output Area and Middle-layer Super Output Area population or household count which breached established thresholds

Changes were made where there was a change in the OA, LSOA and MSOA population or household count which breached established thresholds. If they were now too big in population size or household count, they were split into smaller areas. If their population size or household count had become too small, they were merged with a neighbouring area.

Change to a Local Authority District boundary

Changes were made where the Local Authority District (LAD) containing the OAs, LSOAs and MSOAs had changed its boundary since the statistical geographies were created or updated, and no longer aligned with the OA, LSOA and MSOA boundary.

Changes to ward boundaries

Changes were made in some wards where the boundaries had changed since the original creation of the OAs, the ward statistics calculated using the OA best-fit method were no longer a good match with the new ward boundaries.

The Office for National Statistics (ONS) guidance states that 97% of 2011 COAs in England and Wales were unchanged against the 2021 census. This does not necessarily mean that 97% of our claimants’ geography allocations will remain the same because: 

• claimants are not necessarily spread evenly across COAs 

• we publish at a range of different geographical levels, which may be differently affected by changes to COAs 

Compared to previously published tables, we expect differences to be minimal for higher-level geographies, such as region and local authority. The differences will become more visible with lower-level geography breakdowns, for example lower super output area (LSOA). 

When converting to 2021 COAs, for the majority of Official Statistics, the historic data has been reprocessed through the CIS Address History Database. This provides the most accurate COA held for that individual (at the specific point in time). Where it was not possible to process the historic series in this way, the 2011 COAs were mapped to the new 2021 COAs. Where a 2011 COA had been split into multiple new COAs, these were mapped into the new COAs using a proportional allocation. This will have a minimal impact for higher-level geographies, caution should be taken when comparing historic data at a lower geography level. 

Further Information on ONS geography is available here:  Open Geography Portal.