If you think of high-density cities, you may think of pollution, poverty and moral decline. But the reality, according to new research in urban studies, is that these cities offer residents more economic opportunities and upward mobility. Analyzing data on urban sprawl and economics, the researchers found that high-density urban areas were correlated with dramatically higher levels of upward mobility. As the compactness of a region doubles, they write, “the likelihood that a child born into the bottom fifth of the national income distribution will reach the top fifth by age 30 increases by about 41 percent.”