Mapping local food deserts

The USDA's Economic Research Service has released a map of our nation's food deserts. They classified census tracks as food deserts if they were both-low access--meaning "a significant number or share of individuals in the tract is far from a supermarket"--and low-income. They defined low income at the level of census tract using the following criteria:

The tract’s poverty rate is greater than 20 percent; or
The tract’s median family income is less than or equal to 80 percent of the State-wide median family income; or
The tract is in a metropolitan area and has a median family income less than or equal to 80 percent of the metropolitan area's median family income.

The map lets you change layers so you can see just the low-income tracts if you want. You can also set the low-access threshold to 0.5 miles for urban residents which dramatically increases local food deserts:

So what do you think gentle readers, is this an accurate way to assess the presence of food deserts?

Hat/Tip Sarah K.