The United States is of special interest in connection with the study of all aspects of regionalism, owing to its vast area, roughly three-quarters that of the whole of Europe, forming one political and economic unit; its rapid modern development and transformation from a producer and exporter of primary products, to a dominantly manufacturing country absorbing the great bulk of its own agricultural production; the great and rapid growth of large metropolitan cities; the recent development of federal enterprise in place of the "rugged individualism" of the nineteenth century; and the development of principles of nationwide planning based on the conception of regional development. Two chief problems in the field of regional planning have received much attention in recent years. First, there is need for the conservation and scientific development of the country's natural resources, and second, changes have been brought about in the social structure by the increasing dominance of city life, made possible, above all, by the advent of the automobile, which in the United States is not a sign of affluence, but a first claim for every citizen. The boundaries of the constituent States of the Union and their divisions -- county and township -- are entirely arbitrary and there is need for the creation of new units, large and small, more in conformity with conditions of living and organization.
Planning in the United States is based on the existing administrative units. The city is in many ways inadequate as such a unit, and the metropolitan district or the county has been adopted frequently in its place. The metropolitan unit includes the city and its nearest satellite towns and the contiguous urban and rural districts. It is not the same as the metropolitan district of the Census, and its boundaries cut across county and even State boundaries. The chief example is that of the New York Region. The county with a city as its centre is a second type of unit, and is adopted by many planning organizations. It has the great advantage, as against the metropolitan district, of being a single administrative unit. Two additional areas, larger than the above, are also used for planning, namely, the State itself, and a large area cutting across State boundaries within an arbitrary limit. In many ways the State is a good unit for planning, primarily because it is an existing political unit. It is a good unit for the study of natural resources and conservation problems. The collection of basic data, the formulation of a plan, and the eventual carrying out of the plan are also facilitated by State arrangements, but the planning of the many problems of the State demands that its regional contrasts should be given full recognition. The Tennessee Valley Authority governs the best known area of the second type, the boundaries of the region being the watershed of the Tennessee river.