Use 2020 Decennial Census population

## Summary

This is meant to be a place to document and discuss technical or conceptual issues related to the use of 2020 Decennial Census population counts.

## Notes

* The [P1 and P2 tables][SF1] (i.e., counts by race/ethnicity) were released in August-September 2021.
* You can get at them via http://data.census.gov.
* If you prefer to work with the FTP-hosted, legacy-format files, scroll down on the above page, and you'll find Legacy Format Support Materials, including some import scripts.
* The set of 2020 Census tracts is not identical to the set of 2010 tracts. So you'll likely want to download 2020 tract geometries too.
* Some tracts were split, for example, due to reaching sizes larger than the target of ~4k residents.
* Same goes for blockgroups and blocks.
* There are official 2010 → 2020 crosswalks available, at least for tracts.

[SF1]: https://www.census.gov/programs-surveys/decennial-census/about/rdo/summary-files.html#P1