Moving to a new city or moving to take a job used to be a much more common rite of passage for young people than it is today. Bloomberg reports that the mobility of people aged 25 to 34, a group that has been much more likely to move in the past, is down to 20.2 percent—only one out of five. That’s the lowest level since that data started being collected in 1947.

From Bloomberg:

Economists and demographers say a combination of relatively low-paying opportunities, the burden of student loans and an aversion to taking risks explains the reluctance to relocate. Student-loan debt rose $114 billion in the year ended in December to $1.08 trillion, according to the Federal Reserve Bank of New York. The decline in mobility among young adults “is economically significant,” said Chris Christopher, director of consumer economics for IHS Global Insight Inc. in Lexington, Massachusetts. “It is a lot more expensive to get started, to move, to find a job. In terms of social mobility, job mobility, overall geographic mobility, they are not doing as well as their parents and grandparents.”

That’s not to say that millennials aren’t moving at all. Though the numbers of people relocating might have gone down, millennials are still nearly twice as likely to relocate than other age groups. But with limited well-paying job openings across the country, staying close to a social safety net seems to be a more secure option.

The young people that are moving seem overwhelmingly to prefer denser areas to the suburbs. For a more visual approach for migratory data (that isn’t limited to millennials) check out Chris Walker’s data visualization from last winter of where people were moving in 2012.