The Metabolism of the Urban Web
Writing in Metropolis, Salingaros and Mehaffy explain there theory that "[a] city comes alive only when it is a network that connects many different types of urban activities and nodes.":
"This means that the traditional, mixed-use city is alive, precisely because of its inclusivity of distinct functions, different scales, and different dynamics - which holds as long as one of them doesn't destroy the others. Every diverse place and function should catalyze other essential urban functions, and this is what keeps the network connected and keeps its flows going."
Sprawl, on the other hand, "because of its stretched and fragmented network geometry, requires enormous expenditures of energy: it is, in fact, the most energivorous urban invention in history."