This site sets two census years side by side for one place, and shows what changed between them.
Every figure comes from an open, official source: the 1961 and 2021 censuses through Nomis, mid-year population estimates from the Office for National Statistics, national indicators from the World Bank and Our World in Data, temperature from the Met Office, and boundaries from the ONS Open Geography Portal and Natural Earth. Nothing is modelled here, and nothing is estimated beyond what the original publisher estimated.
It draws no conclusions. The figures are presented with their sources and their caveats, and the reader decides what they mean. Where two publishers disagree, both numbers are shown rather than one being chosen quietly: the world population figure differs by about 0.4% between Our World in Data and the World Bank, and the page says so.
Where a comparison cannot be made honestly, it is not made. Persons per room is published for 1961 and would be the most evocative measure in the set, but the 2021 equivalent measures households against a bedroom standard, which is a different thing. It is left out rather than presented as a like-for-like change.
At present the site covers the world, six continents, the United Kingdom and fourteen English counties, across six census years from 1961 to 2021. The county list is being widened, which is careful desk research against the 1974 boundary reform rather than a technical task. See how places are matched for why that is slow.