Not just one census
In many respects the census is thus a ‘bottom up’ exercise that has its physical expression as the ground truth at small area level.
What do we mean though by ‘small area’ as this is a rather subjective term and one that varies by context and over time? The UK censuses, whilst occurring simultaneously in all parts of the UK (except this time when Scotland will be conducted a year later!) is actually conducted separately by three different agencies – the responsible body in England indonesia rcs data and Wales is the Office for National Statistics (ONS), in Scotland the National Records of Scotland (NRS) and in Northern Ireland the Northern Ireland Statistics and Research Agency (NISRA).
As you might suspect, that means there are inevitably subtle differences in e.g. terminology – the smallest census geographical unit of recording in England & Wales and Scotland is the ‘Output Area’ whilst in Northern Ireland for 2011 the comparable geographical unit was referred to as ‘Small Areas’!
Each agency defines the census geographies used for their country and the methodology and thresholds it uses to derive them.
All however, attempt to capture population characteristics at a geographical level which ensures the anonymity of individual census respondents – that’s always been the case with the census but in an era of Cambridge Analytica/Facebook privacy paranoia it’s not surprising that the security of peoples responses to quite personal questions cannot be stressed enough.