Population-Density Maps of the United States: Techniques and Patterns

Abstract

The construction of an isarithmic map of population density involves a number of problems. In the solution of these problems several techniques were applied, the most important of which was the use of the frequency graph as a guide in the selection of isarithms. Others were the adaptation of the nomograph for the computation of densities and the development of the spot height concept. The decision to use counties rather than minor civil divisions as the areal units of distribution was based on preliminary tests. Two trial maps of population density in Wisconsin were constructed, one based on minor civil divisions, the other on counties. The first map was found to be unsatisfactory, because the minute detail resulting from the use of such small units complicated the picture and tended to obscure the broader patterns. One reason why the use of minor civil divisions blurred the pattern is that townships containing towns or cities loomed high above surrounding townships that had no agglomerations. Thus, because the comb was so fine, areas with even small agglomerations were caught in the sifting and received recognition. In other words, minor civil divisions are of too small an areal magnitude to show gradations of population density for as large an area as the United States. However, such distributions are helpful as guides in the bending of county isarithms when it is necessary to bring out the more densely settled parts of a county. In the construction of the map of the minor civil divisions of Wisconsin a nomograph, was used to reduce acres (in which the areas of the divisions were given) to square miles and to calculate density per square mile in a single operation (Fig. i):