Calvin F. Schmid

Basic Problems, Techniques, and Theory of Isopleth Mapping*

Abstract * Acknowledgment is made to Lloyd Kirry and Gloria Austin for their assistance in drafting the charts. The authors also are indebted to their colleagues, Z. William Birnbaum and Douglas G. Chapman of the Department of Mathematics, John Sherman of the Department of Geography, and Stuart C. Dodd and George A. Lundberg of the Department of Sociology for a critical reading of the manuscript.

Generalizations Concerning the Ecology of the American City

T HIE PRESENT paper is an attempt to formulate a number of generalizations concerning the internal structure of the large American city. In planning this study every effort was made (i) to select a relatively large, statistically comparable and representative group of American cities; (2) to utilize relevant, comprehensive, and reliable quantitative and other data; and (3) to follow systematic and rigorous techniques in analyzing these data. The basic data for this study were taken from the series of census tract bulletins prepared by the U. S. Bureau of the Census in connection with the sixteenth decennial census taken as of April i, 1940. The primary sample consists of 20 American cities of comparable size. In developing a model for an analysis of this kind it was felt that the results could be invalidated if the group of cities selected did not possess some degree of statistical comparability. Accordingly, cities that were within a relatively narrow total population range and at the same time did not vary widely in the average size of census tracts were included in the primary sample. It will be observed from Table I that in total population these cities range from approximately 200,000 (Dayton, 2I0,7I8) to 500,000 (New Orleans, 494,537); the mean population size of census tracts varies from approximately 3,600 (3,585 for Louisville) to 5,Ioo (5,I46 for Birmingham).1 In