Abstract
In a preliminary stage of a complete hierarchical regionalization, a limited number of digraphs are generated by applying thresholds to a doubly standardized 1965–1970 US intercounty migration table. The strong components—sets of mutually reachable vertices—of each digraph are determined by an efficient algorithm. The results indicate that the broadest migration bases are possessed by a pair of Southeastern Florida counties (Dade and Broward); a pair of Chicago area counties (Cook and Du Page); the District of Columbia; and Pierce County, WA, which has a strong concentration of military installations. Several two-county Standard Metropolitan Statistical Areas; the four counties of Hawaii; and most of Connecticut; as well as most of Rhode Island are found to function as migration regions. Though no contiguity constraints are imposed, the clusters—especially relatively small ones—are, as a strong rule, connected. A null hypothesis that these clusters are random can, using asymptotic approximations in this 3140-unit analysis, be rejected. Under an assumption of symmetric linkages, a systematic tendency for counties to have broad migration bases is exhibited.
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