The Large Retailer Access Map (LRAM) was formerly referred to as the Food Access Research Atlas (FARA). FARA now includes two maps, LRAM and the SNAP-authorized Retailer Access Map (SRAM). The two maps rely on different underlying data and methods, so the data sources and technical methods for each are described separately.
The LRAM methods were described in detail in the ERS report Low-Income and Low-Foodstore-Access Census Tracts, 2015–19. LRAM uses retailer location data from 2019. Estimates were aggregated to the census tract level and 2010 census-tract boundaries were used.
The LRAM uses supermarkets, supercenters, and large grocery stores as proxies for the complete set of stores selling a wide variety of healthy foods at affordable prices.
Information on the location of supermarkets, supercenters, and large grocery stores was obtained from two directories—Store Tracking and Redemption System (STARS), which has stores authorized to accept SNAP (Supplemental Nutrition Assistance Program) benefits, and stores in TDLinx, a NielsenIQ directory.
The TDLinx store list is a running list of stores open on June 15 of each year. The directory of SNAP-authorized stores is extracted from the STARS database, which is maintained by the USDA’s Food and Nutrition Administration (FNA; formerly Food and Nutrition Service).
For this analysis, the directory only included authorized stores in the system as of June 15, 2019.
STARS superstores/supercenters are very large supermarkets, “big box” stores, superstores, and food warehouses that are primarily engaged in retail sales of a wide variety of grocery and other store merchandise.
STARS supermarkets are establishments commonly known as supermarkets, foodstores, grocery stores, and food warehouses primarily engaged in retail sale of an extensive variety of grocery and other store merchandise, with 10 or more checkout lanes with registers, barcode scanners, and conveyor belts.
A STARS large grocery store carries a wide selection of the four staple food categories.
About 110 STARS stores were not classified in any of these 3 categories, but upon matching to a store in TDLinx and further inspection through Google Maps and store websites, these stores appeared to be full-service grocery stores with all major grocery departments and weekly sales fliers.
TDLinx uses different store classifications that are more expansive than STARS. TDLinx stores include those in the following subcategories: Grocery Conventional; Grocery–Limited Selection; Grocery–Supercenter; Grocery–Natural/Gourmet; Grocery–Warehouse; and Mass Merchandisers.
LRAM excluded military commissaries and warehouse club stores. Although such stores offer a wide variety of foods and accept SNAP benefits, military commissaries are only accessible to a select group of individuals and club stores are only available to those who pay an annual membership fee, which may be a barrier for people with income constraints.
Drug stores, dollar stores, and convenience stores were also excluded. SRAM includes all SNAP-authorized stores, including drug stores, dollar stores, and convenience stores that are authorized to accept SNAP. FNA estimates show 84 percent of SNAP redemptions were at supermarkets, supercenters, and large grocery stores in 2019. These stores are included in LRAM.
Spatial analysis, string matching, and manual review methods were used to merge the STARS and TDLinx datasets to construct a combined-store directory. This combined directory encompasses all the supercenters, supermarkets, and large grocery stores from each dataset, with duplicates eliminated to avoid double counting.
This matching process identified STARS and TDLinx stores within a 1/3-mile radius of one another or within the same ZIP Code. An automated string-matching algorithm was used to identify exact or similar store name-address matches, which were subsequently verified manually.
Foodstores from either the STARS or TDLinx systems—without a match in the other system—were included in the final combined directory, totaling 45,233 foodstores in the 2019 merged directory. Most foodstores (36,425) were in both data sources. Of the remaining stores, 5,170 were exclusive to TDLinx and 3,638 were found only on the STARS list.
Data on population and characteristics were obtained from the Census Bureau 2010 Decennial Census. Information on income and household vehicle availability was obtained from the Census Bureau 2014–18 American Community Survey (ACS).
Population data were from the 2010 Census because ACS data for these characteristics—though available at the census tract level—are less precise. Population counts, occupied housing unit counts, and other population characteristics (i.e., age, race, and ethnicity) from the 2010 Census were allocated to 0.5-kilometer-square grids.
For income and vehicle access, tract level 2014–18 share estimates of housing units without vehicles and the share of individuals below 200 percent of the Federal poverty line were multiplied by the 2010 housing-unit counts and population counts, respectively, to estimate the number of households without vehicles and the number of people with income at or below 200 percent of the poverty level.
Because median income cannot be downcast to the grid cell level, the definition of “low income” for individuals differs from the definition of low income for census tracts. For individuals, the share of the population at or below 200 percent of the Federal poverty level was used to get closer to the more inclusive tract-level definition of low income.
These numbers and shares were then similarly aggregated down to the 0.5-kilometer-square grid level to provide a fuller picture of population distribution within a census tract so access and populations could be described.
Finally, to estimate whether a tract is low income, 2014–18 ACS tract data were used to directly measure whether the tract:
- has a poverty rate of 20 percent or greater;
- is at or below 80 percent of the greater Metropolitan Statistical Area (MSA) median family income or the State’s median family income; or
- has a median family income at or below 80 percent of the State’s median family income if outside of a MSA.
This was the same measure of low-income census tracts used for eligibility for the U.S. Department of Treasury’s New Markets Tax Credit (NMTC).
To estimate if a tract is low access, the number and share of people more than 0.5 or 1 mile (urban areas) from a foodstore or 10 or 20 miles (rural) was estimated based on the location of foodstores relative to the grids.
Both number and share are used to determine low-access status to accommodate tracts with (1) low populations but where a substantial portion of the tract has low access and (2) with a large number of people who are low access but with only a small share of the total tract population.
Urban census tracts are areas with more than 2,500 people, and rural areas are sparsely populated areas with fewer than 2,500 people. These estimates were aggregated at the tract level for all grids within a tract.
The same criteria for demarcating low access used in LRAM were applied for each of the four measures of low income and low access (LILA):
LILA 0.5 and 10 miles: Low income census tracts where a significant number (at least 500 people) or share of the population (at least 33 percent) is more than 0.5 miles from the nearest supermarket, supercenter, or large grocery store if in an urban area or more than 10 miles if in a rural area.
LILA 1.0 and 10 miles: Low income census tracts where a significant number (at least 500 people) or share of the population (at least 33 percent) is more than 1.0 mile from the nearest supermarket, supercenter, or large grocery store if in an urban area or more than 10 miles if in a rural area.
LILA 1.0 and 20 miles: Low income census tracts where a significant number (at least 500 people) or share of the population (at least 33 percent) is more than 1.0 mile from the nearest supermarket, supercenter, or large grocery store if in an urban area or more than 20 miles if in a rural area.
LILA vehicle access 0.5 and 20 miles: Low income census tracts where a significant number of housing units (at least 100) do not have a vehicle and are more than 0.5 mile from the nearest supermarket, supercenter, or large grocery store; or low-income census tracts where a substantial number or share of people (at least 500 people or 33 percent) are more than 20 miles from the nearest store.
Vehicle availability is defined in the ACS as the number of passenger cars, vans, or trucks with a capacity of 1 ton or less kept at the home and available for use by household members. The number of available vehicles includes those vehicles leased or rented for at least 1 month, as well as company, police, or Government vehicles that are kept at home and available for nonbusiness use. This indicator was applied equally to both urban and rural census tracts.
These measures are estimated and mapped to give researchers and other data users additional ways to consider food-access limitations for census tracts.
| Data | Data Source | Source geographic level |
|---|---|---|
| Store directory | 2019 TDLinx and 2019 STARS | Latitude and longitude coordinates |
| Total population | Census 2010 | Block |
| Housing units | Census 2010 | Block |
| Vehicle access | ACS, 2014-2018 | Block group |
| Income | ACS, 2014-2018 | Block group and tract |
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STARS = Store Tracking and Redemption System. Note: U.S. Department of Commerce, Bureau of the Census 2010 Decennial Census counts of the total population and number of housing units are used even though 2014–2018 U.S. Department of Commerce, Bureau of the Census American Community Survey (ACS) estimates are available for both. The researchers used the decennial estimates instead because of high standard errors in the ACS estimates. Income and vehicle access data are not available from the decennial census, so the most recent version of ACS data, 2014–18 was used. Source: Compiled by USDA, Economic Research Service. |
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