on network, even though some trucking and warehousing is counted separately as part of transportation. Within the Retail Information about the Internet's physical layer is drawn from Russ Haynal's ISP page at http://navigators.com/isp.html. A list of ISPs is provided at http://www.thelist.com/. Exchange point information is given at EP.net, http://www.ep.net/ep-main.html. Networks in Telecommunications sector, some large retail chains also engage in their own wholesale distribution activities. 2. Social and Business Networks Social and business networks, although not the subject of our analysis, are closely related to communications and transportation networks. Social networks are mech- anisms that distribute wealth, transmit information, facilitate business transactions, and form personal relationships. Social networks have been popularized by the idea of six degrees of separation, which refers to the high likelihood that any two members of a society are connected by fewer than six social ties. Fred Jones of Peoria, sitting in a sidewalk café in Tunisia, and needing a light for his cigarette, asks the man at the next table for a match. They fall into conversation; the stranger is an Englishman who, it turns out, spent several months in Detroit. "I know it's a foolish question," says Jones, "but do you by any chance know a fellow named Ben Arkadian? He's an old friend of mine, manages a chain of supermarkets in Detroit "Arkadian Arkadian " the Englishman mutters. "Why, upon my soul, I believe I do! Small chap, very energetic, raised merry hell with the factory over a shipment of defective bottle caps." "No kidding!" Jones exclaims, amazed. "Good lord, it's a small world, isn't it?" (Milgram 1967, p. 61) Although the classic study by Milgram may well be an urban myth (Kleinfeld 2002a, 2002b), the interaction of social connections quickly widens the number of social contacts of individuals to encompass a significant share of the population. Social networks are composed of the individuals in a society and the rela- 