Central place hierarchies have been the traditional basis for understanding external urban relations. However, in contemporary studies of these relations, a new emphasis on urban networks has emerged. Rather than either abandoning or extending central place thinking, it is here treated as representing one of two generic processes of external urban relations. Town-ness is the making of ‘local’ urban hinterland relations and ‘city-ness’ is the making of ‘non local’ interurban relations. Central place theory describes the former through an interlocking hierarchical model; this paper proposes a central flow theory to describe the latter through an interlocking network model. The key difference is the level of complexity in the two processes.