Ancestors

Written by Eldan Goldenberg on 2024-08-09 at 21:22

I have a new favourite geospatial open data bug: US Federal Register 220519-0117 "Change to County-Equivalents in the State of Connecticut".

Sooo... a thing I'm working on for a client is to show various sorts of demographic data at the US Census Tract level, to serve as context layers for the main thing we're building. Most of them come from the 2020 Census, and are straightforward enough to handle: one set of geometries with consistent IDs that all the stats tables can be joined by. (1/?)

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Written by Eldan Goldenberg on 2024-08-09 at 21:24

There are a couple that are drawn from the American Community Survey, which uses 5-year averages to make up for its comparatively smaller sample size in each year. Since the latest 5-year window started before the 2020 Census, they have to be mapped as 2010 Census Tracts. So far so good.

I noticed that the entire state of Connecticut was missing from one of those layers, so I had to investigate. Sure enough, it's in the data table, so what's going wrong here? (2/?)

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Toot

Written by Eldan Goldenberg on 2024-08-09 at 21:26

I learned that there are two distinct sets of FIPS codes (if you don't know what a FIPS code is, all that matters here is that it should be unique and consistent). One of our data sources was consistent with the Tract geometries, and had Tract names like "Census Tract 1001, Fairfield County, Connecticut". The other had different codes, and names like "Census Tract 1001; Greater Bridgeport Planning Region; Connecticut"

Argh. (3/?)

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Descendants

Written by Eldan Goldenberg on 2024-08-09 at 21:31

Once I found that Federal Register announcement I could piece it together. From 1960 until 2022, the US Census Bureau was using outdated labels for subdivisions within Connecticut. Starting in 2022, they now use the up to date planning region names, which have been issued new FIPS codes because they don't have a perfect 1:1 correspondence with the old counties. The problem for me is that while the 2018-2022 ACS 5-year estimates have to use 2010 Tract geometries, they use the 2022 codes. (4/?)

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Written by Eldan Goldenberg on 2024-08-09 at 21:36

I think I can see how to work around this by just making another lookup table to translate between the two sets of codes. But I wonder if anyone's run into this before and has any better ideas.

And if you have run into this before, do you know if any Tract geometries were changed retroactively, or is definitely just the codes?

Oh, and I forgot to link to the Federal Register announcement itself: https://www.federalregister.gov/documents/2022/06/06/2022-12063/change-to-county-equivalents-in-the-state-of-connecticut

(5/5)

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Written by Eleanor Saitta on 2024-08-10 at 01:53

@eldang

Seeing like a sufficiently large state

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