This paper aims to contribute to the development of a general network theory for the social sciences. This ambition comprises an attempt to a) formulate, and illustrate with historical examples, a general hypothesis about the relation between a contiguity and a network principle for spatial development, and to b) use the concept of interaction costs to illuminate the genesis and shaping of networks, the interaction between and within them, and implications of the fact that networks have different durability and potential for change. An attempt is made to break interaction cost-generating factors down into groups according to their potential for change. The concept of affinity is viewed as a part of the aggregate relationship between homogen...