The metadata is: State name, County name, County FIPS code, Core Based Statistical Area (CBSA) id, CBSA title and Metropolitan/Micropolitan Statistical Area (MSA) name.
Note that this data.frame contains duplicates, because some ZCTAs span multiple Counties and States.
Data comes from the US Census Bureau's 2010 ZCTA to County Relationship File (https://www.census.gov/geo/maps-data/data/zcta_rel_download.html), 2010 ZCTA to Metropolitan and Micropolitan Statistical Areas Relationship File and the Core Based Statistical Areas (CBSAs) and Combined Statistical Areas (CSAs) Metropolitan and Micropolitan Delineation files (http://www.census.gov/population/metro/data/def.html).
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