In a country as large as the United States there are many great contrasts in physical conditions, historical development, economic and cultural conditions, cutting across the artificial State boundaries. Such regions have already been the subject of much scientific investigation as ends in themselves and as a means to the solution of particular problems. Physiographic regions have been the special contribution of American physical geographers. Geographers and agricultural specialists are concerned with "agricultural regions", determined on the basis of common systems of farming. Sociologists have elaborated the concept of metropolitan or city regions, based on the spheres of influence of the principal cities, as a framework for the understanding of many fundamental social and economic problems of the day that are associated with city life.
The National Resources Committee suggests a regional division for planning problems in connection with natural resources, which corresponds closely with the accepted agricultural regions. The United States Census Bureau uses a threefold division into North, South and West, with subdivisions, bringing the total number of divisions to nine, though these statistical divisions rarely correspond with the other geographical units. An interesting, and what will probably be an extremely useful type of region, is the manufacturing or industrial region to which geographers have recently given attention in America. Each of these types of homogeneous region is distinguished by a particular range of characteristics and therefore forms a useful basis for the investigation of particular problems.