Reference
Last updated on 2026-10-17 | Edit this page
Glossary
- Census tract
- A small census area of about 1,200 to 8,000 people (4,000 on average). The unit used by the Food Access Research Atlas.
- Coordinate reference system (CRS)
- The system that links map coordinates to places on Earth, identified by an EPSG code such as EPSG:4326 (latitude and longitude) or EPSG:26916 (UTM zone 16N, in meters).
- Food Access Research Atlas
- The USDA Economic Research Service’s tract-level data on food access. In July 2026 it was reorganized into the Large Retailer Access Map and the SNAP-Authorized Retailer Access Map.
- Food desert
- An area where residents have limited access to affordable, nutritious food, usually because they have low income and live far from a supermarket. The USDA’s formal term is a low-income, low-access (LILA) tract.
- Food swamp
- An area with many fast food and convenience outlets relative to healthy food options.
- GEOID
-
A census geography’s identifier. For a census tract it has 11
characters: state (2), county (3) and tract (6). Called
CensusTractin the Food Access Research Atlas. Keep it as text. - Large Retailer Access Map (LRAM)
- The original Food Access Research Atlas, renamed in July 2026. It measures distance to supermarkets, supercenters and large grocery stores, using 2019 store data and 2010 census tracts.
- LILA (low income, low access)
- A census tract that is both low income (by the New Markets Tax Credit rule) and low access (many residents live beyond a distance threshold from a large food store).
- Low access
- At least 500 people, or a third of a tract’s population, live beyond a set distance from the nearest supermarket (for example, 1 mile in urban tracts or 10 miles in rural tracts).
- Low income
- A tract with a poverty rate of at least 20 percent, or a median family income at or below 80 percent of the state (or metropolitan area) median.
- Network analysis
- Analysis of movement along a network, such as roads, for example finding shortest paths or service areas.
- New Markets Tax Credit (NMTC)
- A U.S. Treasury program whose definition of a low-income community is used for the “low income” part of LILA.
- OpenStreetMap
- A free, volunteer-built map of the world. The Expert notebook uses it for supermarket locations, and the grocery access case study’s store points come from it.
- QField
- A free, open source app for collecting field data on phones and tablets, using projects prepared in QGIS.
- Service area
- The part of a network that can be reached from a starting point within a given distance or time.
- Shortest path
- The route between two points along a network with the lowest total distance (or time).
- SNAP
- The Supplemental Nutrition Assistance Program, the largest U.S. food assistance program.
- SNAP-Authorized Retailer Access Map (SRAM)
- A map added to the Food Access Research Atlas in July 2026. It measures distance to any brick-and-mortar store authorized to accept SNAP, using 2025 store data, 2020 census tracts, and both straight-line and driving distance.
- Urban and rural tracts
- In the Atlas, a tract is urban if its population-weighted center lies in a Census urban area, and rural otherwise. Urban and rural tracts use different distance thresholds.