A “human construct” that is often of considerable size has substantial internal unity or homogeneity, which differs in significant respects from adjoining areas. Regions can be classed as formal (homogeneous), functional, or vernacular.
The formal region, also known as a uniform region, has a unitary quality derived from a homogeneous characteristic. The United States is an example of a formal area. The functional part, also called the nodal region, is a coherent structure of areal units organized into a functioning system by lines of movement or influence that converge on a central node or trunk. A major example would be the trading territory served by a large city and bound together by the flow of people, goods, and information over an organized network of transportation and communication lines. Vernacular or perceptual regions possess regional identity, such as the “Sun Belt,” but share less objective criteria in the use of this regional name.
General areas, such as the major world regions in this text, are recognized based on overall distinctiveness.