Phys.org [phys.org]:
Defining the boundaries that separate metropolitan areas has major implications for research, governance, and economic development. For instance, such boundaries can influence allocation of infrastructure funding or housing subsidies. However, traditional methods to define metropolitan regions often hamper meaningful understanding of communities' characteristics and needs.
Drawing on methodologies from network science, He and colleagues have now developed a new method of defining metropolitan areas according to census commuter data. They organized all 3,091 counties in the contiguous United States into an interconnected network, with the number of commuters who cross county lines determining the strength of connections between counties. Notably, unlike other studies that have used commuter data to define metropolitan regions, they also accounted for within-county commuting.
Portland, Oregon has created a regional planning authority, Metro [wikipedia.org], similar to this approach.