The Distribution and Concentration of Population in the United States, 1900-2000

Spatial Gini coefficients are used to analyze the distribution and concentration of population in the U.S. by decade from 1900 through 2000. The analysis first uses states as units of observation and compares the results with those obtained from several other countries also using state or provincial data. These results show that the regional distribution of population in the U.S. has become more even from 1900 to 2000, and that countries range widely in the spatial concentration of their populations. Next, the analysis uses U.S. counties as the unit of observation to analyze population density distributions for the entire country and for each state. The U.S. national population has become more spatially concentrated across counties from 1990 to 2000, and state populations have also become more concentrated at the county level in three out of four states in the U.S. since 1900. An analysis using Massachusetts data suggests that counties are sufficiently small in size to capture the underlying changes in population density relevant at the urban level. Regressions are then explore the determinants of the level and change of population concentration within states for the most recent decades.