The measures vary: straight-line or road distance to the nearest supermarket, household vehicle access, income, or some combination. Thresholds that make sense in a city do not transfer to a rural county, and two studies using different cut-offs can disagree about the same street. Treat any map of "food deserts" as an argument about a definition, not as a finding.
The word itself is contested, because "desert" suggests emptiness where the actual problem is usually the mix and the price of what is available — convenience stores and takeaways where a full grocer used to be. Talking directly about distance, cost and transport is more precise than the metaphor.
It matters for mapping because the gap only becomes visible when grocers, markets, food banks and kitchens are recorded on the same map: absence is legible only against everything that is present. See what is mapped near you.
