The role of hierarchical proximity in migration and population growth: Urban shadow versus urban synergy effects

In this paper we explore how various locational characteristics interact with the population size of settlements to influence the domestic net migration component of population growth in the United States. More specifically, we hypothesize that the attractiveness of a county to migrants is affected by three factors: (1) size class: the county's inclusion within the boundaries of an urban agglomeration of a particular population range; (2) centrality: the county's relative location within its own agglomeration, that is, whether it contains the high-density core or encompasses lower-density suburban or exurban territory; and (3) hierarchical proximity: the location of the county's own agglomeration with respect to other agglomerations of higher order within the urban hierarchy. This third, situational component constitutes the major focus of the paper. After briefly demonstrating the concept of hierarchical proximity within a hypothetical Christallertype (marketing principle) central place city system, we present some illustrative empirical findings from the late 1990s. The evidence suggests that two types of situational effects appear to operate, depending on the size classes involved. We conclude that hierarchical proximity influences local-scale growth through a blending of both 'urban shadow' (migration-depressing) and 'urban synergy' (migration-enhancing) factors.