'Food Deserts' or Mirages?
How many people live there?

30 Jul 2011 in Regulatory Science, Information Quality

Sometimes an urban "food deserts" is in fact a mirage because of a significant error in the data or a cramped, unrealistic definition of "low access" that disregards nearby stores in adjacent census tracts.

Only 7 census tracts in Washington, DC are identified as "food deserts." In one case, the reason is not a lack of access so much as the government's cramped definition of an acceptable grocery store. In one other case, the reason is the government's definition disregards large grocery stores in adjacent census tracts that lie within one mile of where people actually live. For the remaining five census tracts, no large grocery stores appear to be nearby under any reasonable definition of the term. But these census tracts are predominantly industrial. 

Let's look at Washington DC's seven census tracts designated as "food deserts." 

It's not obvious that the total number of low income persons designated as living in a "food deset" is particularly large. Washington DC has a population of about 600,000; if these designations are accurate, it means only 3% of the DC population is both low income and without access to a large grocery store with fresh produce. If so, a lack of access cannot be the explanation for increasing obesity rates.

And 3% appears to overstate the proportion of the population that is low income and lacks access. The last census tract on this list ('9809) is similar to the one in the Mount Vernon VA area examined yesterday. There is a large grocery store within one mile of a substantial fraction of the tract's residents. This grocery store (a Giant Supermarket) is located in an adjacent census tract and circled in red. Each of the blue arrows denotes a one-mile radius from the store. 

Census tracts '9100 and '9101 are shown in the satellite map below. Most of this land area is industrial, so it's not surprising that it lacks large grocery stores.

There are small neighborhoods with housing units located on the north side of tract '9101. The red diamond marks a small cooperative grocery store that specializes in organic and vegetarian foods--preciselly the kind of foods that Mrs. Obama promotes. The store is a few blocks beyond the edge of the census tract nearest where people live. There should be little question that it meets the intent of the First Lady's program even if it does not satisfy the technical (but arbitrary) definition of an acceptable grocery store.

 Below is a street view of the market.

View Larger Map

The remaining four census tracts are shown in the map below. There are few food stores located within the boundaries of these tracts and there appear to be no large grocery stores nearby. They qualify as "food deserts," but they are "deserts" on many other margins as well. Much of this land is industrial or vacant. 

Mrs. Obama seeks to encourage large grocery chains like Wal-Mart to open stores in these areas. Under even the most favorable conditions, however, it's not clear whether enough people live here to justify the fixed costs. Moreover, some of these neighborhoods have conditions that are far from favorable, including relatively high crime rates.

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