Location theory, that had been separately developed in Germany and North America in the early 20th century, and the theory of external economies from "localized industries" (as described in Alfred Marshall's Principles of Economics (1890)) formed the theoretical basis of regional economics, which has played a central role in regional science.
According to Vinod Dubey (1964), Harvey Stephen Perloff, who co-authored State and Local Finance in the National Economy (with Alvin Harvey Hansen) and Regions, Resources, and Economic Growth (with Edgar S. Dunn, Jr., Eric E. Lampard, and Richard F. Muth), denied the possibility for any break-up of regional studies or regional science into "parts parallel to the disciplines employed."
The second approach is to conform with the definition of Lionel Charles Robbins (1932: 15), stated as "Economics is the science which studies human behaviour as a relationship between ends and scarce means which have alternative uses," for the economic problems occurring in regions.
Drawing from the definition of regional economics as the system of the scholarly answers to the question "What is where, and why--and so what?"
in An Introduction to Regional Economics (New York: Alfred A. Knopf, 1971; 3rd ed., 1984) by Edgar M. Hoover and Frank Giarratanai, and from Dubey's (1964: 29) definition of regional economics as "the study of differentiation and interrelationships of areas in a universe of unevenly distributed and imperfectly mobile resources with particular emphasis in application on the planning of the social overhead capital investments to mitigate the social problems by these circumstances," it is definable as the study of the systems of how (much) and where to produce and redistribute what using scarce resources or public goods.