1/ Nerdy thread... I recently put together this tool for exploring @ONS statistical geographies & administrative regions for England & Wales. It's one of various prototypes that we're working on in the #DataVis team in thinking how to visualise @Census2021 https://bothness.github.io/geo-explorer/ 
2/ Since joining @ONS a few months ago, I've been trying to make sense of the MANY geographies are used to report data across the UK, from neighbourhood level all the way up to national level, and to be honest it's been a challenge. Here's a list from the 2011 Census...
3/ The smallest "statistical building block" for census data in England & Wales is an Output Area, covering around 100 households. These areas are so small that there are over 180,000 of them, and they don't even have names, only 9-digit codes like E00080085
4/ These tiny areas are then clustered together into Lower-layer and Middler-layer “Super Output Areas”, known as LSOAs and MSOAs, which have slightly more memorable names like "Southend-on-Sea 014" and "Southend-on-Sea 014C"
5/ MSOAs (& occasionally LSOAs) are also used outside of census years for reporting "small area” statistical data. Eg. my colleague @fryford created these maps at MSOA level for recent @ONS datasets on deprivation https://fryford.github.io/imdmap/  & #Covid19 deaths https://www.ons.gov.uk/peoplepopulationandcommunity/birthsdeathsandmarriages/deaths/bulletins/deathsinvolvingcovid19bylocalareasanddeprivation/deathsoccurringbetween1marchand17april#middle-layer-super-output-areas
6/ The @commonslibrary helpfully put together a set of more recognisable (unofficial) names for MSOAs, based on the neighbourhoods, wards or parishes that they cover, to help make them a bit easier to make sense of. "Southend-on-Sea 014" becomes "Kursal" https://visual.parliament.uk/msoanames 
7/ Going back to the geography explorer, when we zoom out further, we start to see more recognisable higher level geographies, like local authority districts, regions and, finally, countries https://bothness.github.io/geo-explorer/ 
8/ But... Going back to the list at this top of this thread, there are alson a TON of other official @ONS geographies, including electoral wards, parliamentary constituencies, built-up areas and the GeoSTAT grid (the list is ordered by the ones people find most useful)
9/ The easiest way to get hold of @ONS datasets for most of these geographies (especially small area data) is via Nomis https://www.nomisweb.co.uk , but a lot of datasets can also be found via the ONS website https://ons.gov.uk , which should get much easier to use by @Census2021
10/ And... I couldn’t possibly end this thread without mentioning the fact that these geographies only cover England & Wales. Scotland and Northern Ireland data is reported using a whole host of other geographies administered by @ScotStat and @NISRA
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