The Geography of Knowledge Relatedness and Technological Diversification in U.S. Cities

U.S. patent data and patent citations are used to build a measure of knowledge relatedness between all pairs of 438 major patent classes in the USPTO. The knowledge relatedness measures, constructed as the probability that a patent in class j will cite a patent in class i, form the links of a patent network. Changes in this U.S. knowledge network are examined for the period 1975 to 2005. Combining the knowledge network with patent data for each of the CBSAs in the United States permits analysis of the evolution of the patent knowledge base within metropolitan areas. Measures of knowledge relatedness are employed to explain technological diversification and abandonment in U.S. cities.