(Emile Wamsteker/Bloomberg)

As the number of Americans living in poverty has grown since 2000, the shape of that poverty has shifted in some crucial ways. Elizabeth Kneebone and Alan Berube at the Brookings Institution have extensively documented that poverty is growing more suburban, spreading into communities historically short on the resources and institutions to combat it.

At the same time, poverty has also been concentrating. The poor, in other words, increasingly live alongside the poor in a growing number of neighborhoods with alarming rates of poverty. As of the latest 2008-2012 American Community Survey data, 5.4 million Americans under the poverty line were living in census tracts with poverty rates of 40 percent of more.

As Kneebone writes in a new brief: "This trend indicates that an increased share of poor individuals today face the 'double burden' of not only their own poverty, but also the disadvantages of those around them."

In some parts of the country, this concentration of poverty is staggering. In metropolitan McAllen, Tex., for instance, 50 percent of the region's poor population lives in a "distressed neighborhood," or a census tract where the poverty rate is 40 percent or higher. In Fresno, Calif., 40 percent of the local poor population lives in distressed neighborhoods. In Milwaukee, Toledo and Detroit, it's around 30 percent. From Kneebone's analysis, here's a map of the 100 largest metro areas (interactive version with rankings here):

Share of the poor population living in neighborhoods with poverty rates of 40 percent of higher, 2008-2012:


Brookings Institution

The picture is even more stark when we look at poor populations living in census tracts with a poverty rate of 20 percent or more (it's about 92 percent in McAllen, Tex.).

Share of the poor population living in neighborhoods with poverty rates of 20 percent of higher, 2008-2012:


Brookings Institution

Here's a closer look at how this picture has changed in metropolitan D.C.:


Brookings Institution

And in a city that's seen even more dramatic change in just a decade: