Using data from Science-Metrix, a bibliometric consulting firm that licenses data from journal aggregators like Elsevier?s Scopus and Thomson Reuter?s Web of Science, Olivier Beauchesne build an intricate map of scientific collaborations between cities all over the world, between 2005 and 2009.
As Olivier explains: "...if a UCLA researcher published a paper with a colleague at the University of Tokyo, this would create an instance of collaboration between Los Angeles and Tokyo. The result of this process is a very long list of city pairs, like Los Angeles-Tokyo, and the number of instances of scientific collaboration between them."
The brightness of the lines is a function of the logarithm of the number of collaborations betweena pair of cities and the logarithm of the distance between those same two cities.
You can also see a high-resolution version of the map.