Scottish Longitudinal Study
Development & Support Unit
Consistent areas through time for Scotland (1981-2001)
Researchers regularly need to standardise their data to make reliable comparisons. However, standardising geographical units is often overlooked, possibly because users are unaware of subtle changes in the configuration of geographical areas (e.g. census output areas). There are a number of methods available to create standardised, or consistent, geographies, but most methods require the use of areal interpolation techniques, which inevitably incur error – especially when the population is not evenly distributed across a zone. Moreover, there are very few examples of consistent geographies based on small areas.
As part of his PhD research at University of St Andrews, Daniel Exeter developed a geographical boundary file, known as Consistent Areas Through Time, (CATTs), that enables reliable comparisons of social data from 1981, 1991 and 2001 census data. Rather than using an apportioning or areal interpolation technique to create a consistent geography, a merging strategy was used, which meant that whenever a source zone (e.g. 1991 OAs) overlapped more than one target zone (e.g. 1981 EDs), the affected target zones were merged.
The merging process linked the 17,767 1981 EDs, 38,254 1991 OAs and the 42,604 2001 OAs onto one common boundary file containing 10,058 CATTs. More information regarding the construction of the CATTs can be found from the ONS population trends article The Creation of Consistent Areas Through Time (CATTs) in Scotland, 1981-2001 (PDF 819KB).
You can download the Lookup Tables containing information for aggregating data from 1981 EDs, 1991 OAs, or 2001 OAs, to the CATT level here (ZIP 545KB).