Mari Gallagher gets a Google alert every time someone uses the term “food desert” online. That’s because she popularized the term — used to describe locations where it’s harder to find fresh produce and other healthy options than fast food or processed goods — in a landmark 2006 study that revealed as many as 650,000 Chicagoans were then living without easy access to healthy food.

Thanks to new retail options and other changes, that number has shrunk to around 383,000, according to a 2011 report issued by Gallagher and her team. Still, she says, you’d be shocked at how hard it can be to find “a banana that doesn’t look like it got in a fight with another banana” or “produce that doesn’t come out of a can” in many Chicago neighborhoods. (A young woman who tweeted that she now lived in a food desert because “Whole Foods didn’t stock her favorite kind of sushi anymore” had missed the point, Gallagher adds.)

Gallagher’s food desert analysis produced grim findings that are now an accepted part of the dialogue around food access— stats like African-Americans in Chicago have to go twice as far as white residents to find a grocery. But all of Gallagher’s research starts with the most simple question: What retail exists where and what does it sell? It’s harder to answer than you might think.

The U.S. Department of Agriculture, which runs the Supplemental Nutrition Assistance Program (SNAP) more commonly called “food stamps,” has its own way of classifying the various kinds of stores that sell food. The government agency used to make those classifications public, Gallagher says. Now it doesn’t (although it still catalogs participating outlets in its searchable online database).

Even when the USDA’s taxonomy was publicly available, Gallagher found that their classifications weren’t always accurate. While doing research in Detroit in 2007, Gallagher says she came across places with names like “Jimmy Jack’s Liquor Shack” that were labeled as “medium-sized grocery stores.”

Then, she says, the USDA would release “stats like ‘84% of all food stamp dollars were spent in grocery stores in 2010,’ when first of all, it depends on how you’re coding a supermarket.” Gallagher argues that inaccurate labeling of retailers makes it much harder to combat food insecurity. “We think it’s a bigger deal in low-access areas,” she says. “We’re very concerned about these specific areas where there are so many bad apples and so few mainstream [food retailers].”

All of this categorical confusion means that Gallagher has to be a super sleuth: Step one in her process is figuring out where the stores are, and what they sell.

Some places are easier to assess, like national or regional chains that have predictable stock. “A Jewel is a Jewel,” for example, and Gallagher says she’s never seen a 7-11 that sells enough produce to qualify as a “mainstream” retail outlet based on her team’s definition.

It’s much tougher when it comes to assessing corner stores, the kind of mom-and-pop operations that are often the closest retail option for people in food deserts. With these kinds of places, Gallagher sometimes goes undercover.

“You pretend like you’re a customer,” she says. “You call and say, ‘We’re new in town and we don’t know that much about your store. I’m wondering for my kid’s lunch — do you have these things: apples, oranges, fresh spinach?’” She gets mixed reactions from such sleuthing. “Sometimes people will yell at you, ‘We don’t have any of that stuff!’ And hang up on you,” she says. “It happens a lot.”

Sometimes when Gallagher hits the pavement in places like Washington, D.C. or Alabama, she’ll come across stores where it’s not clear if they’re out of business or merely closed. So she asks around.

“I’ve done things like find the closest social service agency, a church or daycare, something across the street,” she says. She gives them the same “new in town” routine, and often gets good information. “People will say, ‘Oh, that’s mostly a liquor store,’ or ‘It doesn’t open ‘til 1,’ or ‘You know what? It’s closed.” Ask, Gallagher says, and “you’ll know more.”

Gallagher says that she feels “a little bad operating under a pretext,” but argues it’s for a good cause.

“If you told them you were a researcher, it would be too complicated,” she says. She loves having to reclassify corner stores when, in response to efforts like a Chicago-area public health initiative that provides seed money and refrigeration equipment, they start stocking more produce.

But, she says, the most important thing is to stay neutral — to figure out the honest truth of what’s available at a given store and what’s not.

“If you get angry, you’ll lose your ability to sort fact from fiction,” she says. “You’re in the eye of the storm. Some people will love what you find, some people will hate it. But you’re trying to uncover the best information you can, to keep your neutrality, without spin one way or the other.”

Gallagher spoke at the Jane Addams Hull-House Museum in March, and shared some of the back story of her ongoing research. In the audio above, she discusses the challenges of getting such accurate info and explains why sleuthing in the field is such a crucial part of her process.  

Dynamic Range showcases hidden gems unearthed from Chicago Amplified’s vast archive of public events and appears on weekends. Mari Gallagher spoke at an event presented by the Jane Addams Hull-House Museum in March. Click here to hear the event in its entirety.

Gallagher will appear at an event called Chicago’s Food Deserts: How you can have an impact, at the Peggy Notebaert Nature Museum on Tuesday April 17 from 7 to 9 p.m.

Correction: An earlier version of this story mistakenly attributed the term “food desert” to Gallagher. She popularized the term in her 2006 report, but did not coin it.