Officials at the U.S. Department of Agriculture said the vast majority of people use motor vehicles to shop for groceries, so vehicle availability is a key indicator of supermarket access.
Users of the atlas can view whether a census tract has a significant number of housing units that are far from supermarkets for those who don't have vehicles.
The original version of the Food Desert Locator implemented a single measure of food deserts -- low-income areas where a significant number of residents is far from a supermarket. "Far" was more than 1 mile in urban areas and more than 10 miles in rural areas.
The updated application includes estimates for Alaska and Hawaii, which were not available in the original version. In addition, data for all U.S. census tracts are viewable and available for download at http://www.ers.usda.gov/data-products/food-access-research-atlas/about-the-atlas.aspx#.UUEp-ByG2w4.
Previously only data for food-desert census tracts were available, officials said.
Some census tracts that contain college campuses and other large institutions technically meet the low-access and low-income conditions, but were likely to provide dining services where residents eat on a regular basis. To provide more context for these areas, users can view an indicator that measures whether a census tract has a high share of people living in "group quarters."
Estimates in the atlas are based on a 2010 list of supermarkets, the 2010 Decennial Census and the 2006-10 American Community Survey.