The U.S. is a large country and is itself a changing part of a much larger and changing global economy. How the nation as a whole is fairing economically varies from time to time, but there also are wide variations in economic conditions and trends at any point in time within the nation. Some places and areas may do very well while others struggle. Fundamentally, economic activity and the economy itself are organized around the activities of people and the many roles they play in it; including as employees and employers, investors and managers, sellers of products or services and consumers, and as taxpayers and public decisionmakers. By viewing it geographically, the uneven distribution of the U.S. population can be easily seen. There’s a tremendous amount of regional variability in the density of people and the size and scope of major population centers or major "nodes" of economic activity.
Just as with population, the types and levels of economic activity distribute themselves in uneven, irregular, and ever-changing patterns across this large landscape. The size and character of market areas vary greatly from place to place. And while aspects of the larger economy operate almost without geographic bounds, many types of economic activity and many businesses can exist or prosper only within the confines of fairly well-defined geographic market areas. Most people will regularly drive only so far to work each day; ordinarily 50 miles or less. People will drive only so far to buy groceries or to receive routine medical care and the number and array of medical services offered in a particular place depend upon the character of the surrounding trade and service area.
Sub-state regional economies are formed within the overlay
of many different regionally-defined marketplaces that vary by type of good,
service, or activity. And the regional variability of these marketplaces is
heavily reflected in the pattern of population distribution. Furthermore,
patterns of population growth or decline are heavily influenced by changes
in the economy.