title: Geographic routing in social networks.
abstract: We live in a "small world," where two arbitrary people are likely connected by a short chain of intermediate friends. With scant information about a target individual, people can successively forward a message along such a chain. Experimental studies have verified this property in real social networks, and theoretical models have been advanced to explain it. However, existing theoretical models have not been shown to capture behavior in real-world social networks. Here, we introduce a richer model relating geography and social-network friendship, in which the probability of befriending a particular person is inversely proportional to the number of closer people. In a large social network, we show that one-third of the friendships are independent of geography and the remainder exhibit the proposed relationship. Further, we prove analytically that short chains can be discovered in every network exhibiting the relationship.
authors.affiliation: Department of Mathematics and Computer Science, Carleton College, 1 North College Street, Northfield, MN 55057, USA. dlibenno@carleton.edu
authors.forename: David
authors.initials: D
authors.lastname: Liben-Nowell
authors.forename: Jasmine
authors.initials: J
authors.lastname: Novak
authors.forename: Ravi
authors.initials: R
authors.lastname: Kumar
authors.forename: Prabhakar
authors.initials: P
authors.lastname: Raghavan
authors.forename: Andrew
authors.initials: A
authors.lastname: Tomkins
mesh_terms: D000465:Algorithms; D033062:Friends; D005843:Geography; D006801:Humans; D011156:Population Density; D011336:Probability; D012919:Social Behavior