About the Atlas
Limited access to supermarkets, supercenters, grocery stores, or other sources of healthy and affordable food may make it harder for some Americans to eat a healthy diet. Expanding the availability of nutritious and affordable food by developing and equipping grocery stores, small retailers, corner markets and farmers’ markets in communities with limited access is an important part of the First Lady's Let's Move! initiative.
There are many ways to define which areas are considered "food deserts" and many ways to measure food store access for individuals and for neighborhoods. Most measures and definitions take into account at least some of the following indicators of access:
- Accessibility to sources of healthy food, as measured by distance to a store or by the number of stores in an area.
- Individual-level resources that may affect accessibility, such as family income or vehicle availability.
- Neighborhood-level indicators of resources, such as the average income of the neighborhood and the availability of public transportation.
In the Food Access Research Atlas, several options are available to describe food access along these dimensions.
ERS's Food Access Research Atlas was built using Environmental Systems Research Inc. (ESRI) ArcGIS Server technology. The background topographic and satellite maps, as well as the address locator service, were also provided by ESRI.
Measures of food access
The original version of the Food Desert Locator implemented a single measure of food deserts—low-income areas where a significant number or share of residents is far from a supermarket, where "far" is more than 1 mile in urban areas and more than 10 miles in rural areas.
In the new Food Access Research Atlas, food access indicators for census tracts using ½-mile and 1-mile demarcations to the nearest supermarket for urban areas, 10-mile and 20-mile demarcations to the nearest supermarket for rural areas, and vehicle availability for all tracts are estimated and mapped. Users of the Atlas can view census tracts by food access indicators using these different measures, including the original food desert measure, to see how the map changes as the distance demarcation or inclusion of vehicle access changes.
Additional indicators of food access
The vast majority of people in the United States use motor vehicles to shop for groceries, so vehicle availability is a key indicator of supermarket access. Users can now view whether a census tract has a significant number of housing units that are far from supermarkets and do not have vehicles.
Some census tracts that contain college campuses and other large institutions technically meet the low-access and low-income conditions, but are 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".
Data availability and updates
Estimates in the Atlas are based on a 2010 list of supermarkets, the 2010 Decennial Census, and the 2006-10 American Community Survey. The updated application now 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 (previously only data for food-desert census tracts were available).
Component layers for mapping tool
To be considered a food desert under the original definition or the additional food access measures, a census tract must be both low income and low access. Users can now view maps that show these two components separately—for example, users can view census tracts that have high numbers or shares of people with low supermarket access, but are not low income.
Changes in methods between 2006 and 2010
Methods used to estimate low-income and low-access census tracts in 2010 are largely the same as methods used in previous estimates. There are however, two notable differences.
First, the 2010 analysis used ½-km-square grids to estimate distances from supermarkets, whereas the previous analysis used 1-km-square grids. The ½-km-square grids are likely to give better estimates of distance to supermarkets; however, this could mean that the estimated distance to stores for some grids changes, even though no change occurred in the location of the nearest store or in the income or location of the population. It is expected that the greater precision of the ½-km-square grids will have a small net impact on estimates of distance to the nearest store.
Second, a new method for designating whether a census tract is urban or rural was used. In the previous analysis, census tracts were designated as urban if the geographic centroid of the tract was in an urban area or urban cluster according to U.S. Census Bureau definitions. All other tracts were considered rural. The 1-mile demarcation was used to indicate low access for tracts with a centroid in an urban area, and the 10-mile demarcation was used for tracts with a centroid in rural areas. This meant that, for parts of some tracts containing both urban and rural sections, a 1-mile marker was used to assess low supermarket access if the geographic centroid of the tract was urban, even though part of the tract was rural (and vice versa—if the centroid was in the rural part of the tract, the 10-mile marker was used).
For the 2010 analysis, the population-weighted centroid was used to designate a census tract as urban or rural. This should improve estimates of low-access tracts in areas with rural and urban overlap because it more accurately applies the urban 1-mile marker to urban areas and the 10-mile marker to rural areas. However, this change likely results in changes in the low-income and low-access status of some census tracts.
For additional information, see Documentation.
How is the Food Access Research Atlas related to the Food Environment Atlas?
The Food Access Research Atlas maps and provides selected food access indicators for census tracts. The Food Environment Atlas provides a wider set of statistics on food choices, health and well-being, and community characteristics. While the Food Access Research Atlas provides information at the census-tract level, the smallest geographic level of data in the Food Environment Atlas is the county. The Food Environment Atlas also has an advanced query tool that allows users to identify and map counties sharing the same degree of multiple indicators.
Economic Research Service (ERS), U.S. Department of Agriculture (USDA). Food Access Research Atlas, http://www.ers.usda.gov/data-products/food-access-research-atlas.aspx.