America's geography of wealth: the shrinking urban middle class visualised

The economic fates of diverse cities such as San Francisco, New York and Detroit would seem to be vastly different - but they share a common thread

Over the last half-century, the story of America's cities is a tale of booms and busts. New York and tech hubs like San Francisco - once cities in financial distress - have transformed into economic powerhouses. At the other extreme, one-time prosperous manufacturing cities like Detroit now find themselves in economic turmoil.

Viewed in isolation, the economic fates of these cities would seem to bear little resemblance to each other. However, they all share a common thread: since 1970 these cities, like nearly every other major American city, have experienced a "hollowing out" of the middle class.