The size and density of cities confers considerable economic advantages. Denser cities are seed-beds of innovation and productivity improvement, as Jane Jacobs long ago argued. Pioneering studies of "urban metabolism" by Geoffrey West and his colleagues at the Santa Fe Institute find that as metro areas get larger their metabolic rate essentially speeds up, making them more productive and inventive
The environment benefits from density and size as well. Larger, denser cities are cleaner and more energy efficient than smaller cities, suburbs, and even small towns. Ecologists have found that by concentrating their populations in smaller areas, cities and metros decrease human encroachment on natural habitats. Denser settlement patterns yield energy savings; apartment buildings, for example, are more efficient to heat and cool than detached suburban houses. Urban households emit less carbon dioxide than their suburban and rural counterparts. In his book Green Metropolis, David Owen lauds the dense, concentrated built environment of Manhattan – where most people live in apartments and use mass transit — as the greenest place in America. When it comes to greenness, size matters; as urban regions grow their populations, the rate of growth in their emissions actually declines.