  We analyze the entire publication database of the American Physical Society
generating longitudinal (50 years) citation networks geolocalized at the level
of single urban areas. We define the knowledge diffusion proxy, and scientific
production ranking algorithms to capture the spatio-temporal dynamics of
Physics knowledge worldwide. By using the knowledge diffusion proxy we identify
the key cities in the production and consumption of knowledge in Physics as a
function of time. The results from the scientific production ranking algorithm
allow us to characterize the top cities for scholarly research in Physics.
Although we focus on a single dataset concerning a specific field, the
methodology presented here opens the path to comparative studies of the
dynamics of knowledge across disciplines and research areas
