Urban Influence Codes
A list of Urban Influence Codes (UICs) data sets. The 2013 UICs are a classification scheme that further subdivides metropolitan counties by the population size of their metro area, and nonmetropolitan counties by the size of their largest city or town, and includes their proximity to metro and micropolitan areas. This scheme allows researchers to break down county data into finer residential groups for the analysis of trends in nonmetro areas.
USDA Economic Research Service