Methods of mapping migration flow patterns

In this paper, we explore alternative methods for mapping and highlighting the most significant patterns of movement present in a complex system of interregional migration streams. Commonly authors show, for instance, the "ten largest" streams of movement. However, a spatial interaction perspective would lead us to suspect that the streams with the largest absolute numbers of migrants might simply occur for origins and destinations having the largest populations--especially those in close spatial proximity. Using 1994-1995 IRS tax-return data for flows between U.S. states we explore a number of alternative measures that may be used to select the most "salient" streams in the movement system. We examine gross flows, net migration flows, demographic effectiveness (efficiency), transition probabilities, and several new interactance standardizations, and we compare the visual representations that they yield.