The spatial focus of US interstate migration flows

Despite the widespread interest in the changing geographies of national migration regimes, it is somewhat remarkable that no widely accepted measure of the spatial concentration or focus exhibited by such geographies has emerged. We examine four of the most popular indices of inequality in this paper and contrast their performance as measures of spatial focus. Adopting the coefficient of variation as our preferred alternative, we go on to examine the spatial focus of aggregate interstate migration streams in the US over time. Then we consider disaggregations of the migration streams by age, race and nativity, and examine the role of states as national redistributors of these same subpopulations. We find that the migration patterns of the elderly, blacks, and the foreign-borns in general have exhibited levels of spatial focus that exceed those of their young adult, white, and native-born counterparts. With respect to the principal redistributor states, our findings for all subpopulations point to a very few states that persistently reappear in the group-specific classifications. In particular, California is a unique redistributor of the US population, always appearing as an extensive outward or inward redistributor of migrants.