Figure 4. Effect of geographical proximity in the world collaboration and citation networks.

The probability of existence of a link as a function of the distance between two cities in the (A) collaboration network and (B) citation network. Distribution of the ratio of the link weight and product of the strengths of its endpoints in (C) collaboration network, and (D) citation network, against the distance d_ij between the cities. For each distance the average ratio is also shown. The solid line indicates a power law behavior with exponent α = 1.16 ± 0.03 and 0.77 ± 0.02 respectively.