Reproduced from Chetty, et. al, 2018, "Race and Economic Opportunity in the United States: An Intergenerational Perspective"; Note: Location based on where men grew up; Map: Axios VisualsThe fastest-growing cities in the U.S. may be adding lots of jobs for well-off people, but many have low rates of upward mobility for lower-income kids growing up there. And it's especially bleak for black males, according to Raj Chetty, Harvard economics professor and director of Opportunity Insights, a research and policy organization.Why it matters: The extent of racial disparities and economic mobility "is so extreme in the U.S. that it's almost like they're two Americas," Chetty said about the maps above.The places that have the very highest rates of mobility for black men, like Boston, actually have lower rates of upward mobility than the very worst places of upward mobility for white men, like Charlotte.Chetty's research showed that job growth and investment happening in Charlotte and Atlanta, for example, aren't creating opportunities evenly, and black male youths are disproportionately being left behind.What they did: The researchers analyzed outcomes of about 4 million families that moved across neighborhoods and tracked the outcomes of children of low-income parents over 30 years.What they found: Childhood environments are stronger indicators of upward mobility than where individuals go to college or move as young adults.Moving to a better neighborhood at a very young age correlated with much stronger upward mobility as adults. In fact, every extra year of exposure to better childhood environments improved outcomes.Downward mobility is also critical. White men from affluent families are likely to stay affluent as adults. But black men from affluent backgrounds are nearly just as likely to end up in the bottom tier of the income distribution than the top tier."If you think of achieving the American dream as climbing an income ladder for white Americans, it’s more like being on a treadmill for black Americans. Even after you've made the climb up in one generation, there are tremendous structural forces that tend to push you back down in the next generation and you have to make the climb again."Raj Chetty, speaking at the Results for America Summit in Washington, D.C.And the disparities are likely to worsen over the next decade.By 2030, African American workers stand to lose hundreds of thousands of jobs as a result of increased automation, widening the racial wealth gap and weighing down overall U.S. growth, according to a report from McKinsey & Co.The bottom line: A strong national economy only goes so far. The most important factor in determining upward mobility is the conditions in the half-mile radius around where you live, Chetty said."While we often think of the decline of the American dream as a national problem — a challenge we’d like to solve through federal policy solutions — I really think the roots of these issues are at the very local level."Go deeper:Explore the map (Opportunity Insights)Automation to hit African Americans disproportionately (Axios)The punishing reach of racism for black boys (NYT)