There’s not a single county in the United States that has an even balance between the number of extremely low-income residents and affordable and available rental units. Not one.

Suffolk County, Mass., comes the closest. It has the smallest gap, with 50.4 affordable and available units available per 100 extremely low-income (ELI) renter households.

Cobb County, Ga., has the biggest gap, with just 2.8 affordable and available units per 100 ELI renters, according to the Urban Institute, which has unveiled an online map that details the nation’s rental housing crisis. Visitors can click on any county to see how large the affordable housing gap is in the area.

“The Affordability Gap Map is important because it quantifies a pressing public policy problem,” says Erika Poethig, director of Urban Policy Initiatives, at the Urban Institute. “Half of all renters in the U.S. are cost-burdened. That’s a fact which many in the housing field and even beyond know quite well. But where is this burden heaviest, and what policies have been shown to make a difference? That’s the conversation we wanted to facilitate.”

Poethig says “a quick glance shows that some regions, like the South and Southwest, have disproportionately fewer numbers of affordable and available units for extremely low-income households. Other regions, through extensive state and local efforts, have made strides in closing the affordability gap.”

The situation would be much worse if not for federal rental assistance, which assists 3.2 million ELI households, those earning no more than 30 percent of the area median income (AMI), notes the Urban Institute, a nonprofit involved in economic and social policy research.

The map allows users to turn off the federal assistance data to see just how much this resource affects families in every county.

The map has broad reach and translates to a variety of audiences, according to Poethig.

“We know it is being used by advocates, the media, bloggers, and state, local, and federal policymakers and practitioners,” she says. “For example, we have heard from congressional staffers who are interested in key demographic groups or certain parts of the country. It’s also intended to spark conversations and policy action at the local level.”

In addition, the map helps federal policymakers and advocates begin to identify regions that are underserved by federal rental assistance, according to Poethig.

The map is at

Connect with Donna Kimura, deputy editor of Affordable Housing Finance, on Twitter @DKimura_AHF.