"Perhaps the most widely used regional classification system is one developed by the U.S. Census Bureau." Dale M. Lewison, Retailing, Prentice Hall (1997): p. 384. (ISBN978-0-13-461427-4)
"[M]ost demographic and food consumption data are presented in this four-region format." Pamela Goyan Kittler, Kathryn P. Sucher, Food and Culture, Cengage Learning (2008): p.475. (ISBN9780495115410)