Food Deserts: Your Data Needs Work

While perusing twitter, I discovered this tweet on the topic of food deserts:

So, I decided to take a look at where the food deserts are in my adopted town of Lafayette, IN. Before we go any further, let's see how the USDA is defining food deserts:

The HFFI working group defines a food desert as a low-income census tract where a substantial number or share of residents has low access to a supermarket or large grocery store:

• To qualify as a “low-income community,” a census tract must have either: 1) a poverty rate of 20 percent or higher, OR 2) a median family income at or below 80 percent of the area's median family income;
• To qualify as a “low-access community,” at least 500 people and/or at least 33 percent of the census tract's population must reside more than one mile from a supermarket or large grocery store (for rural census tracts, the distance is more than 10 miles).

So, back to Lafayette: according to the food desert locator, apparently there is a "food desert" that begins less than half a mile from the grocery store I personally shop at. This suggests that they need additional granularity in their data - defining the deserts by census tracts presents the problem as much larger (geographically) than it is, and prevents us from seeing where the true problem areas lie. Because I know the area, I know that at least 1/3 of that "desert" is less than a mile from a supermarket, and one block past the north edge is the location of a truly fine farmer's market. This makes me distrust people on the subject of the magnitude of the food desert problem. Get me better data, then we'll talk.