A busy London neighbourhood is not necessarily a populous one

A pavement crowded with office workers or visitors tells you something about activity, but not directly about resident population. The Office for National Statistics defines a usual resident for Census 2021 through residence and intended duration of stay.[21] That is a different measure from the number of people passing through a London neighbourhood during a working day.

For that census, the definition included people in the UK who had stayed or intended to stay for at least 12 months, and people with a permanent UK address temporarily abroad for less than 12 months.[21] A headcount taken outside a station would not apply those rules. Presence and usual residence are related, but they are not the same statistical category.

The observation date also matters. Census 2021 describes people and households on 21 March 2021, rather than providing a live population counter.[21] Reusing one of its figures in a neighbourhood description requires preserving that date. The age of the observation does not make it useless, but it limits what it can establish about conditions today.

Consider a hypothetical district with a major employment centre and relatively little housing. It could attract large daytime crowds without having a correspondingly large resident population. Another area could house many people while drawing fewer visitors. Which measure is useful depends on whether the question concerns residents, demand at a particular hour or the movement of people.

For local comparisons, record the geographic boundary and reference date beside the number. Then name the population concept rather than calling every count “how many people are here.” This approach makes London data more intelligible without mistaking historic census results for current footfall, transport demand or the number of homes available to rent.