This year’s election has forced Americans to take notice of class divisions between workers. And while these divisions may at first ring of lazy stereotypes — the rural Rust Belt worker without a college degree and the coastal urban college-educated worker — they’re rooted in a real dynamic. Many of the most skilled workers — young people with college degrees — are leaving struggling regions of America for cities, specifically for cities in Southern and coastal states.

There are clear economic reasons for their choice. Dense metro areas tend to produce more jobs and make workers more productive. Wages, for all kinds of workers, are also higher.

In theory, these incentives should prompt workers of all levels of education to move to metro areas. But moving outside one’s region is relatively rare these days, and even more rare for someone without a college degree.

Moving is actually quite uncommon in advanced economies. The United States has been one of the exceptions. It has one of the highest rates of internal migration among advanced economies, and it has since at least the middle of the 19th century. A study comparing thousands of American and British census records between 1850 and 1880 showed that nearly two-thirds of American men moved across county lines, while only a quarter of British men did.