Peter Smith provides a legend:
These food deserts (marked in pink above) are places where there is "low income" and "low access"—or places where at least a fifth of the population lives at or below the poverty line and where there isn't a supermarket within a one-mile radius (or within a 10-mile radius in rural areas). All things told, about 13.5 million people nationwide have little or no access to stores selling healthful food.
The Dish 