How is a metropolitan area characterized?

A metropolitan area is typically defined by the presence of one or more urban centers and their surrounding communities that are economically and socially interconnected. The correct choice states that a metropolitan area must have at least one municipality with a population of 100,000. This threshold is used to signify a substantial urban center, reflecting a concentration of population and resources that indicates a significant hub of activity and infrastructure.

This definition is important because it helps in planning, resource allocation, and transportation development, as well as in studies related to urbanization and public policy. Such a population baseline ensures that the character of the area is distinctively urban and that it supports a variety of services, employment opportunities, and cultural amenities that are associated with larger cities.

The other choices do not accurately reflect the standard criteria used to define metropolitan areas. For instance, a population of 50,000 may not adequately capture the complexity and scale of urban interactions, while options focusing solely on urban districts or on specific combinations of municipalities with population requirements do not align with commonly accepted definitions in urban studies.