There's a reason why the world's wealthiest people--people with near-infinite options vis-a-vis the choice of where to make their home--consistently choose to live in the densest areas on the planet. Ultimately, they live in these spaces for the same reason that the squatter classes of Sao Paulo do: because cities are where the action is. Cities are centers of opportunity, tolerance, wealth creation, social networking, health, population control, and creativity.