The economics literature clearly shows that the transmission of knowledge diminishes with physical distance, a factor contributing to industrial clustering. This paper investigates how those distances have stretched over time. We measure the physical distance between collaborating inventors, as...

While it is clear that there has been a "regional inversionʺ in American patent activity over the past 25 years (i.e. relative rise of the Northwest and Southwest at the expense of the traditional invention hotbeds of the Northeast and Midwest), the reason is still open to speculation....