Geographic categories come from the NCHS Urban-Rural Classification Scheme for counties.
Large central metros are counties with cities of a population of 1 million or more that also meet one of the following: (1) contain the population of the largest city of the metro area, or (2) have the whole population contained in the largest city of the metro area, or (3) comprise 250,000 residents of any principal city of the metro area.
Large fringe metros are counties with populations of 1 million or more that did not meet the requirements of large central metros.
Small metros are counties in a metropolitan area of less than 250,000 residents.
Micropolitan counties contain micropolitan statistical areas.
Noncore Rural counties that do not qualify as micropolitan.