SPATIAL AGGREGATION AND INTRANSITIVITY IN U. S. MIGRATION STREAMS.

Earlier papers have drawn attention to the inconsistency between observed migration flows between U. S. states and the predictions of a broad class of spatial interaction models, in that observed flows show frequent intransitivities while the models predict perfect transitivity. The paper compares the properties of flows between the real states with those of county flows aggregated to alternative sets of regions generated using various stochastic processes and satisfying certain objective functions. Intransitivity is affected by the variance in the number of counties per state, but is otherwise largely independent of the particular boundaries chosen. The set of 'states' which minimizes intransitivity is found to consist of strongly heterogeneous regions which lack compactness.