This paper addresses the ecological problem of how a territorial system is organized around a metropolitan center or system of such centers. We hypothesize that accessibility to the metropolitan system is inversely related to the degree of internal heterogeneity or differentiation of nonmetropolitan cities. Measuring differentiation on four variables: industry, occupation, education, and income, we find general support for this proposition. Ecological theory bearing on these problems also suggests that such specialization derives from trade interdependencies that grow with increased accessibility to the total territorial system. We interpret this to mean that the degree of industrial differentiation in a community mediates the relation between accessibility and other dimensions of differentiation. Again, the evidence seems to support this prediction. This paper addresses a key issue in human ecology: how a territorial system is organized around a metropolitan center. It starts from the principle that: focal point in tle territorial organization of the community is its center, for it is there that interdependencies are integrated and administered (Hawley, a:238). A derived proposition is that the friction of space causes the organizing of the center to decline with distance between itself and units within its region of dominance. Organizing influence is a broad term, of course, and this general conceptual approach has spawned many efforts to show that one or another areal characteristic reveals a distance gradient (see, for example, Bogue; Duncan et al.; McKenzie). We take organization to mean the interdependence of functionally specialized parts, a position supported in ecological theory (Gibbs and Martin; Hawley, a). Our hypothesis is that community units on the periphery of a metropolitan system should prove less specialized in function and more heterogeneous in composition than units near the center. The community units to which the present data pertain are nonmetropolitan cities whose territorial organization we see as shaped by their integration in a metropolitan system.