The trouble I have with the report comes from the maps used to convey the District's food deserts, particularly Maps 3 and 4 on pages 15 and 18 of the report. Below is our annotated version of Map 4, "Food Deserts in the District of Columbia."
Click image to view larger map
What seems to have happened in the report is what Mark Monmonier calls a "Blunder that Misleads" in his book How to Lie With Maps. According to the report, the methodology for creating Map 4 is as follows:
Map 4 was developed using poverty data provided by the District of Columbia Office of Planning. The Office of Planning matched census tracts where 51 percent or more of the population lives at incomes below 200 percent of the federal poverty level with those tracts that have below-average access to full-service grocery stores (as identified by Social Compact in Map 3).
The blunder—not a lie but rather a "cartographic fallibility"—is that census block group data is used. Entire block groups are designated as food deserts that a.) have no living residents (cemeteries and parks, etc.), and so do not have much income and require no access to food, or b.) are institutionally used (hospitals, etc.), and so do not have much income but likely provide food on-site. Simply put, nearly 1/4 of the areas designated as food deserts may technically, but not realistically, fit the working definition.
Particularly during this time of increasing unemployment, homelessness, and hunger, advocacy groups across the District and the country are working overtime. Like many others, I want to help in the fight for social justice, but we need to be sure our data are airtight in order to effectively convey our messages.
Cross-posted at Greater Greater Washington.