Core city

In urban planning, a historic core city or central city is the municipality with the largest 1940 population in the present metropolitan area. This term was retired by the US census bureau and replaced by the term principal city, which can include historic core cities and post-WWII cities. Metropolitan areas were no longer considered monocentric, but polycentric due to suburbanization of employment. A historic core city is not to be confused with the core of a metropolitan area which is defined as an urban area with a population of over 50,000 by the US census bureau.