<div dir="ltr"><div class="gmail_quote"><div>The US Census also collects legal / admin boundary information from other entities ( down to things like school districts ). 
<a href="https://www.census.gov/geographies/reference-maps/2021/geo/bas/2021-bas-maps.html">https://www.census.gov/geographies/reference-maps/2021/geo/bas/2021-bas-maps.html</a> because federal money flows according to these boundaries.</div><div><br></div><div>But reallocation of population counts into these is a non-trivial exercise, because at the block / tract level they do everything possible to maintain those from census to census to make time series easier. ( "
 A century of census tract use has shown that census tracts continue to 
be an important geography for the tabulation of decennial census data 
and other statistical programs, and that census tract boundary 
continuity and the resulting census tract data comparability over time 
are of considerable significance to data users." from 

<a href="https://www.census.gov/history/www/programs/geography/tracts_and_block_numbering_areas.html">https://www.census.gov/history/www/programs/geography/tracts_and_block_numbering_areas.html</a> ).</div><div><br></div><div><br></div><div><br>
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