It seems like some of the State Economic Areas should be metropolitan districts. The documentation says “Metro Areas”.
https://usa.ipums.org/usa/volii/seaco…
Wondering if that is the same. (yes, I should just download the data to check but save me the trouble…)
State Economic Areas (SEA) are county based geographies, much like Metropolitan Areas (METAREA), generally built around a central city. Metropolitan Districts (METDIST), however, are constructed of a central city and its surrounding minor civil divisions such as small cities and towns. So, while many SEAs and Metropolitan Districts will share a central city, SEAs use Counties as building blocks to define the larger economic area where Metropolitan Districts use towns and small cities as building blocks. You will see strong overlap between METDIST and SEA for many areas, but they do not often match up perfectly.
I hope this helps.