How places are matched across the years

The hardest part of comparing a place across sixty years is deciding what counts as the same place.

County boundaries in England were redrawn in 1974. A county named on a 1961 census table and a county named today can cover very different ground, so every comparison here rests on an explicit mapping from the 1961 county to a set of modern authorities, and each mapping carries a grade.

The grades

Clean: The same ground in both eras. Rutland and Shropshire are examples. These can be compared directly and are the only ones used in rankings without qualification.
Approximate: Modern authorities aggregated to stand in for the 1961 county. Northumberland is built from Northumberland, Newcastle upon Tyne and North Tyneside. The comparison is indicative, and the page names the authorities it is built from.
Excluded from rankings: No honest mapping exists. Dorset is the current example: Bournemouth and Christchurch were in Hampshire in 1961 and only moved in 1974, but Poole was in Dorset and now sits inside the same modern authority as them, so the two cannot be separated. Including that authority imports about 200,000 people who were never in the county; excluding it drops Poole, which was. Dorset is shown with a warning and left out of any ranking.

Mistakes this catches

Getting a mapping wrong produces figures that look plausible and are not. An early version of this site put Gateshead, South Shields and Sunderland in Northumberland, when all three were in County Durham, and Northumberland appeared to have grown 76%. Corrected, it runs from 824,390 in 1961 to 829,205 in 2021, which is the flat Tyneside story the history supports. The same error placed the Black Country in Warwickshire rather than Staffordshire.

A ranking sorts errors of this kind straight to the top, because the largest movers are the most likely to be artefacts. That is why rankings exclude anything not graded clean or approximate.

Above county level

Countries and continents do not have this problem in the same way. The United Kingdom did not change shape between 1961 and 2021, which is why national figures are exact where county figures need grading. At world and continent level, Russia is counted in Europe by both the United Nations and Our World in Data; the outlines split it at the Urals so that Europe does not render as mostly Siberia, while the population figures are left exactly as published.