=How the National Population is Distributed.=—The people of the United States are very unevenly distributed over the face of the country. Great areas, particularly in the West, have only a few persons to the square mile, while the crowded sections of the largest cities have many hundreds to the acre. Even the rural areas of some states are thickly settled while in others the people are few and far between. Rhode Island is nearly as densely populated as Belgium, having about 566 people to the square mile while many states of the Western mountain region have only seven or eight inhabitants per square mile of territory. The reasons for this uneven distribution are chiefly geographical. The states which have grown most rapidly in population are not necessarily the oldest states but the ones which have the greatest natural advantages in the way of fertile soil, or mineral resources, or harbors and waterways, or favorable climate. People make their homes in those regions where they can best make a living. [Sidenote: Climate affects the density of population.] Favorable climatic conditions exert a strong influence in attracting population. It is an interesting fact, often noted by students of history, that whereas civilization developed earliest in the tropical and semi-tropical zones it has everywhere made its greatest advance in the regions of moderate temperatures and rainfall. Taking the broad strip of country which lies between the thirty-seventh and the forty-fifth parallels of latitude, it will be found that nearly four-fifths of the entire population is concentrated within this mid-latitude area of the United States. And this is the area which, in all probability, will continue to be the most thickly settled. [Sidenote: The center of population in 1920.] The center of population in 1920 was at Whitehall, Owen County, Indiana, a little town of forty-three inhabitants which burst into prominence overnight when the census bureau announced it as the pivot of the nation. By the center of population is meant the point which the greatest number of people could reach with the least amount of travel. This point, at each successive census, has been steadily moving westward following very closely the thirty-ninth parallel of latitude. In 1790 it was at Baltimore, in 1840 in West Virginia, in 1880 in Ohio, and since 1890 it has been moving westward across Indiana.[9] The center of population is a long way from the center of area, the latter being in Northern Kansas not far from the Nebraska border.