IN the agricultural geography of any area two sets of factors are of basic importance: on the one hand, the extent and productivity of the cultivable on the other, the agricultural population. These factors have been measured and mapped in detail for the United States in many different ways, notably on the dot maps published by the United States Department of Agriculture. Such maps, however, tell us little of the relation between the two sets of factors, and it is precisely this relation that is of greatest importance. If the density of farm population varied directly with the productivity of the land, that is, if farms were commonly small in fertile areas and large in poorer areas, we could recognize a principle of compensation as a result of which the fundamental basis of rural economy was more or less equivalent throughout any country. Actually the facts in many cases are just the reverse. For example, the farms in the Kentucky mountains are smaller, not only in extent of land but even in total extent, than those in the Bluegrass region of the same state, and the largest farms in the maturely agricultural areas of the United States are found in the heart of the Corn Belt, in districts of highest crop yields per acre. In order to study this situation for the whole country, and particularly to suggest a basis for more detailed studies of individual areas, the maps here presented were prepared from the county statistics of agriculture of the United States census of I930 (Figs. I, 3, 4). They depict three different attributes of the agricultural land, in each case in proportion to the rural farm population (as distinct from the total rural population). They provide a rough picture of the fundamental situation, namely the amount and productivity of agricultural land per unit of agricultural population in the different regions and districts of the country. No one of the maps alone is adequate, nor indeed are all three together entirely adequate, because of a number of irrelevant factors, as well as inaccuracies, in the basic figures. All three of the maps are affected by the fact that the statistics of farm population take no account of families supported only in part by farming and in part by other activities, notably in mining and urbanized districts. The most reliable of the maps is probably the one showing the ratio of land to farm population. Arable land is the total of cultivated land and cultivable pasture in the census. This ratio, however, takes no account of the differences in productivity within the category of arable land; the very high figures in the Great Plains areas represent large farms on land of very low productivity. On the other hand, there is no allowance for the use of noncultivable land, an important factor in the productivity of the land in the dairy areas of the North and all the mountain areas. The ratio of the value of farmland (not including buildings) to farm population would perhaps be the most significant of the three ratios used if the figures could be taken as entirely reliable, which is hardly the case. Least reliable, perhaps, are the figures for values of products, since these are based in large part on estimates of products consumed on the farm, of which neither the amounts nor the values can be accurately determined. In both of these cases of ratios based on values the figures vary greatly from year
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