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12 cities of 10,000 or more population, it has been determined that the largest system investigated would have to be increased by 14,100 miles.

Any effort to reach a larger number of the cities under 50,000 population than are connected by the recommended system, it is believed, must result in a lowering of the average traffic volume served by the system as a whole. The gain to a few of our smaller cities would, therefore, be accomplished at the expense of a diminishing return in traffic service for the system as a whole. The committee decided this would not be warranted.

The map, figure 3, shows the recommended system in relation to the location of all cities of the several population groups larger than 10,000. This map shows how directly the recommended system joins the larger cities, and the remarkable extent to which most of these cities are served as hubs of their respective regions.

The largest cities not directly connected are shown to be Akron, Canton, and Youngstown in Ohio, but all of these are passed in close proximity. The difficulties that prevent immediate connection of these cities are evident—junction cannot be made without introducing either what appears to be an unwarranted local duplication of routes, or a considerable indirection of approach to the commanding nearby city of Cleveland.

On the basis of the 1940 Census, the Bureau of the Census defined a certain area in connection with each city of 50,000 or more population as a metropolitan district, except that two or more such cities were sometimes included in one district. The number of metropolitan districts totals 140.

The general plan was to include in each district, in addition to the central city or cities, all adjacent and contiguous minor civil divisions or incorporated places having a population of 150 or more per square mile. In some districts, a few less densely populated contiguous divisions were included on the basis of special qualifications. Occasionally only a portion of a minor civil division was included if the division was large in area and had its population principally concentrated in a small section in or near the central city.

The districts defined are, therefore, not political units, but rather areas of the thickly settled territory in and around the country’s larger cities or groups of larger cities. They tend, in general, to be or less integrated areas, with common economic and social, and often, administrative interests. As will be seen from the map, figure 4, the recommended inter-regional system connects directly or passes in very close proximity to all but 10 of these districts.

Location in relation to population distribution.—A statement of the numbers of cities reached directly by the recommended system does not convey an entirely adequate impression of the nearness of approach of the system to the homes of a large proportion of the urban population of the United States. Although only 54.5 percent of all cities of 10,000 or more population are located directly on the system, the aggregate population of these cities is 82.6 percent of the total urban population of the Nation. With slight exception in two