informational role of cities is a primary reason for" their continued existence. This paper formalizes Marshall's theory in a model … of other implications of the theory are corroborated" empirically …

We examine how the spatial and social proximity of inventors affects knowledge flows, focusing especially on how the … two forms of proximity interact. We develop a knowledge flow production function (KFPF) as a flexible tool for modeling … access to knowledge and show that the optimal spatial concentration of socially proximate inventors in a city or nation …

a key empirical prediction of this theory: that inventions in large cities build on newer ideas than inventions in …