It’s not news that people are talking about inequality in America.

President Barack Obama called it “the defining challenge of our time.” Mayors from around the United States (notably New York's Bill de Blasio) used the issue as a way to rally voters. Protests over fast-food workers' wages are happening in multiple cities and San Franciscans are rallying against their “Google Bus” problem.

It’s a national problem being played out in almost every city – but where is the disparity highest?

Researchers from the Brookings Metropolitan Policy program used U.S. Census data to find out for a recent report, using what they call a “95/20 ratio.” That means they take the income of a household in the top five percentiles (i.e., those earning more than 95 percent of households) divided by a household that earns just over 20 percent of the average (the bottom fifth).

“Overall, big cities remain more unequal places by income than the rest of the country,” the report reads. “Compared to national averages, big-city rich households are somewhat richer and big-city poor households are somewhat poorer.”

Plus, some cities are more unequal than others. In Atlanta, for example, the richest 5 percent earned more than $280,000 while the poorest 20 percent earned less than $15,000.

Atlanta, San Francisco, Miami and Boston had the greatest spread between rich and poor incomes.

This map compares cities in terms of the inequality.