The theoretical framework of urban and regional economics is built on transportation costs for manufactured goods. But over the twentieth century, the costs of moving these goods have declined by over 90% in real terms, and there is little reason to doubt that this decline will continue....

Alfred Marshall argues that industrial agglomerations exist in part because individuals can" learn skills from each other when they live and work in close proximity to one another. An" increasing amount of evidence suggests that the informational role of cities is a primary reason for" their...