A new Internet-based mapping tool pinpoints the location of what the U.S. government calls “food deserts.”

The online Food Desert Locator, developed by the U.S. Department of Agriculture’s (USDA) Economic Research Service (ERS), was unveiled Monday.

Simply put, food deserts are areas where people have limited access to affordable and nutritious foods.

Under the government’s definition, which was developed by the departments of Treasury, Health and Human Services and USDA, a food desert is a low-income census tract where either a substantial number or share of residents has low access to a supermarket or large grocery store.

“Low income” tracts are defined as those where at least 20 percent of the people have income at or below the federal poverty levels for family size, or where median family income for the tract is at or below 80 percent of the surrounding area’s median family income.

Tracts qualify as “low access” tracts if at least 500 persons or 33 percent of their population live more than a mile from a supermarket or large grocery store (for rural census tracts, the distance is more than 10 miles).

According to the USDA, about 10 percent of the 65,000 census tracts in the United States meet that definition.  Mostly in urban areas, these food desert tracts are home to 13.5 million people.

The USDA, in a news release, said the tool can be used by policy makers, community planners and others to identify places where public-private intervention might help make fresh, healthy food more readily available, one of the goals of First Lady Michele Obama’s Let’s Move! initiative to address the epidemic of childhood obesity.

The Food Desert Locator is on the Web at www.ers.usda.gov/data/fooddesert.