If cities are the greenest form of human settlement that we could possibly aspire to, Jane Jacobs left us the owner's manual for how to build them. Fifty years ago this month, Random House published The Death and Life of Great American Cities, an extraordinary book in which Jacobs laid out the principles for creating a healthy city. The blocks must be at a human scale, she said. There must be a diversity of activities to keep eyes on the street. The focus of the economy -- of everything -- should be local, typified by Greenwich Village, the Manhattan neighborhood …