Changes in the nature of urban spatial structure in the United States, 1890-2000

This paper documents the long-run trends in the average densities and density gradients of urban areas in the United States. The data show that between 1890 and 2000 the average densities of cities and metropolitan areas rose and fell but that the density gradients of urban areas generally declined monotonically over time. While it is beyond the scope of this paper to estimate the causes of these changes, this paper argues that a complete understanding of the changes in the nature of US urban spatial structures is likely to go beyond the standard explanations based on the monocentric city model such as decreases in transportation costs and increases in household incomes.