A Brief Introduction to Food Deserts

As a still-learning data scientist (as if there were any other kind), I’m always on the lookout for interesting data to fiddle with, in my copious free time. Recently, my fiddling has turned toward the USDA’s Food Access Research Atlas, a resource for the study of food deserts in the US. In the coming months (here’s hopin’), I’ll be posting some of the work I’ve done, but first it’s worth diving into the concept a little.

What, generally, is a food desert?

As a concept, a food desert is pretty simple: a neighborhood with insufficient access to healthy food sources. “Healthy” is the key term here—in general, think places that have a produce section. Grocery stores, supermarkets, etc. You can get a filling meal at the gas station minimart, but it’s not exactly an oasis of healthy eating.

What, specifically, is a food desert?

The USDA actually provides several different possible definitions of a food desert, but they use some form of the following criteria:

  • Distance from sources: how many people in the neighborhood are too far from a healthy food source?
  • Economic factors: is the region considered “low income”? Do the residents lack sufficient transportation resources to reach more distant sources?

In this data, neighborhoods translate to census tracts. An imperfect designation, since these tracts vary widely in size and density, but it enables access to a wide range of demographic statistics.

Low-income tracts have either a poverty rate of at least 20%, or a median income less than 80% of the median from the surrounding area (either the metropolitan area or the state, depending on where the tract lies).

Access is defined by the tract population too far from the nearest source. In urban areas, “too far” can be 1/2 or 1 mile, and in rural areas, it’s 10 or 20 miles. “Low access” indicates that at least 500 people, or 33% of the population, suffer from low access.

Why does income matter?

Of course, even the sufficiently-incomed benefit from proximity to healthy food. But they are also more likely to have the transportation and time resources to travel farther for their groceries.

Poor diet quality is a major source of public health concern in low-income and poverty-stricken communities. The cheapest way to manufacture food is to use low-quality ingredients, chemically preserved, and the cheapest way to make low quality ingredients and chemicals taste edible is to pack them with salt, sugar and fat. Increasing access to fresh food won’t magically make it cheaper, but whatever barriers can be minimized are a step in the right direction.

As a quick preview before I start really diving into the data, here is a look at which regions of Tacoma are considered low income/low access, at the 1 mile (left) and 1/2 mile (right) distances.

4 thoughts on “A Brief Introduction to Food Deserts

  1. On first blush, I look for the data I know and how it is represented on the Map. This doesn’t seem to represent Fred Meyer on 19th and Stevens, or Stadium Thriftway.

    Also interesting is that 38th Street seams to be a boarder region by Pacific Avenue, but there are lots of Produce sources along 38th Street, and the 38th st Safeway. Am I reading this wrong?


    1. I general, I think this is a case of more precise numerical definitions (which are important for some purposes) and somewhat arbitrary borders also leading to some quirks. Any store right on the edge of a tract, like the 19th street Fred Meyer, will by nature have more people further away from it than one right in the middle. If you centered a same-population area around that Fred Meyer it probably wouldn’t get flagged.

      In a later post I’m going to try to map the actual food sources with their 1/2 and 1 mile radii to get a more precise view of what specific areas fall out of range. Census tracts are a useful starting point, because we have a lot of demographic data we can analyze, but they definitely don’t tell the whole story.


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