The complexities of publishing gridded data for the UK European Forum for Geostatistics Krakow – October 2014 Ian Coady Geography Policy and Research Manager Office for National Statistics

Why are we different? No use of grids at the national or sub-national level No use of administrative data in the collection and publication of statistics Historic reliance on administrative boundaries for the publication of official statistics Large user demand for Census microdata on administrative boundaries

But…. It is (partially) understood that the publication of Census microdata at the administrative level is not sustainable due to disclosure issues INSPIRE has given us a common platform and specification for the publication of statistics …and I am here to try promote the interoperability of data at the European level

Output Areas  Created for the 2001 Census  Built around consistent numbers of population and households  Used postcodes as the building blocks  Included a high level of social homogeneity  Some cartographic constraints were used

Geography Policy for National Statistics

Previous work on grids 1km grids provided between 2005 and 2006 Provided by aggregating population estimates from the postcode level to the grids Lack of administrative data sources meant data below postcode level was no longer available ONS has provided data for England and Wales but (we think) Scotland and Northern Ireland have provided data separately

Best-Fitting from Postcode

Research Questions 1) How can the sex and age variables that do not currently exist on the postcode level mid-year population estimates be published? 2) How do the methodologies for publishing gridded population data differ across the devolved administrations of the UK, and how could this approach be harmonised? 3) What is the statistical impact of publishing gridded data at the postcode aggregate level rather than from the microdata? 4) What options exist for visualising gridded population data?

Small Area Population Estimates team no longer produce mid-year estimates at the postcode level To align with the Geography Policy for National Statistics all estimates are now produced at the Output Area level

Best-Fitting from Output Areas

Exact-Fitting from Census Microdata

Grid Methodologies LevelRecordsFrequencySourceAdditional Variables Households23,406,16210 yearsCensusYes PostcodesUnknown No Output Areas 181,408AnnualMid-Year Estimates No

Other alternatives….. Use soil sealing layer (SSL) to produce dasymetric reallocation of population: Small area population data are intersected with the SSL and used to re-weight population counts into settled areas, which are then aggregated to grid cells May offer consistency with broader European practice, but inconsistent with other ONS approaches. Disclosure control attitude unknown and would need to be tested. Offers alternative to postcode use that can no longer be carried out. Use ONS built-up areas layer to produce dasymetric reallocation of population: Variant of previous option but consistent with ONS data sources as uses the Built- Up Areas (BUA) layer instead of SSL. Intersects OA boundaries with BUAs and allocates population to BUAs in proportion to area. Then aggregate to grid cells. Uses only published ONS data, so no additional disclosure risk. Reproducible methodology but needs to be tested.

A country of countries Northern Ireland have disclosure concerns about the disclosure risk of publishing on both the Irish National Grid and the GEOSTAT Grid Both Scottish and Northern Irish Census microdata is stored separately and experience shows accessing this data can be a long and slow process

Sustainable variables Small Area population estimates do not currently include sex or age Increasing use of administrative data could allow this to be included Change to the SAPE processes would be required Would depend on the agreed level of publication but could potentially go further than age and sex

Conclusions Producing UK level grid outputs is possible Producing them from Census microdata is possible but only through Census and the differences between this and the small area population estimates would be noticable Differences in the methodologies of the devolved administrations are superficial but improved data sharing is needed to do this on an ongoing basis Additional variables could be provided on an ongoing basis but only through administrative data that has not yet been integrated into the ONS Statistical Business Process Model

Any questions???