Location matters – enormously. If you’re poor and live in the New York area, it’s better to be in Putnam County than in Manhattan or the Bronx. Not only that, the younger you are when you move to Putnam, the better you will do on average.

Every year a poor child spends in Putnam County adds about $150 to his or her annual household income at age 26, compared with a childhood spent in the average American county. Over the course of a full childhood, which is up to age 20 for the purposes of this analysis, the difference adds up to about $3,100, or 12 percent, more in average income as a young adult.

These findings, particularly those that show how much each additional year matters, are from a new study by Raj Chetty and Nathaniel Hendren that has huge consequences on how we think about poverty and mobility in the United States. The pair, economists at Harvard, have long been known for their work on income mobility, but the latest findings go further. Now, the researchers are no longer confined to talking about which counties merely correlate well with income mobility; new data suggests some places actually cause it.

Consider Manhattan, our best guess for where you might be reading this article. (Feel free to change to another place by selecting a new county on the map or using the search boxes throughout this page.)

It’s among the worst counties in the U.S. in helping poor children up the income ladder. It ranks 175th out of 2,478 counties, better than only about 7 percent of counties. Compared with the rest of the country, it is also bad for rich boys and rich girls. It is relatively worse for poor girls than it is for poor boys. (The low-income population in Manhattan is concentrated in the far northern and southern parts of the borough.)

Here are the estimates for how much 20 years of childhood in Manhattan adds or takes away from a child’s income (compared with an average county), along with the national percentile ranking for each.

“The broader lesson of our analysis,” Mr. Chetty and Mr. Hendren write, “is that social mobility should be tackled at a local level.” Here’s where Manhattan stands among its neighbors.