What would be an example of a formal region?

the rust belt in the united states

"back home"

the commuter bus loop in dallas, texas

the subway system in new york city

An example of a formal region is the Rust Belt in the United States. Three common types of regions are formal regions, which are defined formally by government or other structures, such as cities, states, and mountain ranges; functional regions, which consist of a central place and the surrounding areas that are dependent upon that place, such as a metropolitan area; and vernacular