Hello,
I’m producing some county-level choropleths for each year from the US full-count censuses 1850-1940. I have read that I can use the IPUMS USA variable COUNTYNHG to combine census-level tabulations (eg. employment share by industry) with the NHGIS county boundary files. However, the county boundaries of course change over time, and I have not been able to find for which year (i.e. vintage) of county boundaries the COUNTYNHG variable is for–assuming it is for a single year, and not also changing each year (I was hoping to keep the county boundaries consistent across years). Would this be possible to clarify?
Thank you in advance for the help, and apologies if I missed something in the documentation.
Jacob