Theories of localized knowledge exchange argue that proximity among economic agents in spatial clusters fosters invention and innovation. An alternative perspective stresses interregional collaborative networks in which individuals and groups are embedded in wide-ranging webs of relationships. This article uses social network analysis to explore the changing structures of collaborative systems of intermetropolitan co-patenting in American biotechnology from 1979 to 2009. Results show that intermetropolitan network complexity has broadened and deepened. While inventors in major centers are the foremost collaborators, a dense web of knowledge exchange has emerged that is not singularly controlled by a handful of intermediaries. National linkages have developed, but intense local and regional ties persist. Inventive centrality, magnitude, and patent intensity significantly correlate. Inventors in small areas are obliged to substitute intermetropolitan networks for thin agglomerative economies. An estimate is proposed of the size of biotechnology centers needed to generate agglomerative economies. The system approximates a core-periphery structure with core metropolitan areas strongly tied to one another and to peripheral areas. City systems theory and associated American empirical analyses help interpret results.
