The 2021/22 UK censuses have variously included new questions on gender identity, sexual orientation and past service in the armed forces. the way that acceptability of asking about particular topics changes over time.
The census is always a trade-off between usa rcs data informing contemporary policy questions and the ability to make historical comparisons. This is one of those aspects that makes census-taking an endlessly fascinating exercise.
Geographical challenges
There are multiple factors which change in UK geography over time and need to be reflected in censuses, including:
Reorganisation of local and regional government areas
The changing allocation of land for residential use, such as greenfield and brownfield sites being redeveloped as housing and, less frequently, the clearance of former residential areas
Changing patterns of where people choose to live, such as the huge increases in city centre living across the UK in the last two decades (albeit temporarily reversed by the global Covid-19 pandemic).
For studying how places change over the long term, small area census data are one of the best sources we have.
That said, the small areas themselves can be tricky: if they are updated to best match contemporary patterns of housing and demand for services, they will no longer match those from the previous census. For 2021, changes to output areas in England and Wales are generally being minimised, while Northern Ireland, by contrast, will have entirely new small areas.