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Rh groups, the cities directly connected are the largest of their respective population groups. This is shown in table 3.

A still more graphic picture of the population reasons for choice of the particular routes recommended will be found in figure 5. This shows by dots the distribution of the whole population of the United States, each dot representing a population node of 2,000 persons. Here it will be seen that the various routes not only have their principal local termini or hubs in the larger cities but also pass en route between these hubs, through or very close to the denser clusters of population in small towns and populous rural areas. Indeed, the courses of the recommended routes are shown by this map to be in most instances the inevitable selections, if service of population is to be considered important in the choice.

In a few instances apparent lack of correlation in this respect is evident, and a local shift of the recommended route may be found desirable after further and more intensive study. In such further study consideration should also be given to local adjustment of the recommended routes to a closer conformity, if such be possible, to the larger concentrations of rural population.

That such conformity already exists in large measure is indicated by the map, figure 6, which shows by intensity of shading the gradation of average density of rural population, county by county. Here, again, the remarkable manner in which the recommended routes trace their courses along the country's most populous bands of territory is apparent at a glance. Few if any instances occur in which the recommended route locations can obviously be materially improved, except by excessive multiplication of local mileage.

As further evidence of the advantageous selection of the recommended routes for service of the rural population, the data presented in table 4 show that although the routes traverse only 1,056 or 34.3 percent of the total number of 3,076 counties in the United States