FORTUNE — The global economy has arranged itself around a short list of dominant cities, the endpoints for movement of all kinds: goods, people, money, and, increasingly, packets of digital information. These packets — some trillion bytes a second — travel primarily as light through fiber-optic cable. E-mails, images, streaming movies, and money: millions and millions every millisecond.

We take it for granted that the Internet, as much as any city, has a physical reality. Tracing the movement of a packet of information throughout this geography of fiber-optic cables and data centers casts the global economy in a different light. Keep reading →