U.S. patents have been classified into technology categories at a number of different levels. At the one-digit level there are six categories; at the two-digit level there are 36 categories. On application, every patent is required to cite previous art. The citations to other patents are a patent's "up-citations", while the patents citing a patent are its "down-citations". The net in-flows and net out-flows of citations between technology categories provide insight into trends in technological innovation.
This Demonstration uses the patent citations datasets compiled by B. H. Hall, A. B. Jaffe, and M. Tratjenberg (2001) comprising more than 3 million U.S. patents (and more than 16 million citations) granted between January 1963 and December 2002. This Demonstration allows the user to select the time frame for the selection of the data, and to consider either up- or down-citations. The arrows in this Demonstration are scaled by the number of net citations between the two technology categories over the selected time period, while the size of the yellow disks representing each category are scaled by the number of patents granted during that time period.