Superlinear Scaling for Innovation in Cities
  Superlinear scaling in cities, which appears in sociological quantities such as economic productivity and creative output relative to urban population size, has been observed but not been given a satisfactory theoretical explanation. Here we provide a network model for the superlinear relationship between population size and innovation found in cities, with a reasonable range for the exponent. 
Samuel Arbesman, Jon M. Kleinberg, Steven H. Strogatz