Hi, Can anyone point me to information about how ACS handles Census Tract boundaries for 5-year estimates when there's a boundary change within the 5 years. (i.e. a 2021 estimate has 3 years that would be using 2010 Census boundaries, and 2 years using 2020 Census boundaries). We know that these 5-year estimates are released in 2020 boundaries, but we're unsure how ACS apportions the pre-2020 data into the 2020 Census Tract boundaries. Thanks!
I think you're referring to geog units of the home addresses of ACS respondents? The ACS Design and Methodology report has only 1 sentence that I could find: "The first step is to update the current residence geography for 2016-2020 data to 2020 geography."
Census Bureau has the geolocated addresses of ACS respondents. It's all geocoded point locations, so then Census Bureau can reidentify the (new) tracts and BGs etc for the millions of pre-2020 survey responses. That's it.
If instead you're referring to the questions ACS asks about place-of-work or migration from 1 year previous... that's more complicated. See the ACS Design and Methodology report, section 10.7 (Multiyear Data Processing).
My coworker created this swipe app that compares the tracts: https://www.arcgis.com/apps/StorytellingSwipe/index.html?appid=a6a6636753ef48f6b7b8167cdb590e21, along with an explanatory blog about it: https://www.esri.com/arcgis-blog/products/arcgis-living-atlas/mapping/acs-2016-2020-updated-boundaries/ The blog post really focuses on impacts on maps, but also links to a lot of Census info.