For years, cities like Detroit built fancy towers and development projects in the hopes that this would revive the downtown core. But cities thrive because they host quality conversations, not because they have new buildings and convention centers. The cities that have thrived over the past few decades tend to have high median temperatures in January (people like warm winters and other amenities). But even cold cities like Chicago can thrive if they attract college grads. As the number of college graduates in a metropolitan area increases by 10 percent, individuals' earnings increase by 7.7.