For the many complicated ways that people shop for groceries – Giant has cheaper chicken soup, Whole Foods has better broccoli, the checkout line at Publix is shorter at night – research models of how people get their food are, for the most part, remarkably simple.
"The literature has been primarily assuming that people shop in the supermarket that’s closest to their home," says Anju Aggarwal, a research associate with the University of Washington's Center for Public Health Nutrition. Or, maybe, you hit the supermarket or corner store that's next to your office. "All of the research has been based on that assumption around the work neighborhood or the home neighborhood."
And so-called "food deserts" are usually defined by that first hypothesis: If you haven't got a grocery store in the neighborhood where you live, then you might as well have no meaningful access to food at all. As we've previously written, this thinking is starting to evolve to incorporate how people move around a city on any given day into a clearer picture of their food geography. In fact, earlier research from Washington's Center for Public Health Nutrition, surveying 2,000 people in Seattle's King County, found that few people shop at their nearest supermarket, and many travel quite far.
"There are people who live next to Whole Foods, but they’re driving to Fred Meyer," Aggarwal says (Fred Meyer is a lower-cost chain). And there are people who live next to Fred Meyer but drive across town to Whole Foods, where they perceive that the food is healthier and the organic selection better. "For you and me," Aggarwal says, "even though we might be living next door to each other, our food environment might be very different."
So how do you really begin to understand what a person's true food environment looks like? Well, you can stick GPS tracking devices on hundreds of shoppers and watch where they go over the course of a week.
Aggarwal and colleagues, working with the university's Urban Form Lab, recruited 493 representative adults from across King County and asked them to do just this (while also keeping a travel diary and answering questions about their food preferences and shopping habits). The researchers will now be analyzing the unprecedented data set, collected over the last two years as part of a study funded by the National Institutes of Health. But as a first swipe at understanding it, they asked Schema Design (the Seattle studio behind some other transportation visualizations we've highlighted) to map the results.
This video shows all 493 people moving as white dots around the city over a single week (their movement, captured at varying times, was compressed onto the map as if they were each tracked during the same week). The stationary blue dots are supermarkets that were visited by the sample group at some point during the study.
Effectively, this video illustrates the full extent of grocery opportunities available to people over the course of their weekly movement. The white dots don't necessarily stop to shop at the stores in this visualization. The video also records all the stores they passed, within 100 meters, during the day. The more people come into close proximity to a store, the larger its blue dot becomes over the week.
Schema also made a second video tracking the speed of movement by all 493 people during a single day. In this video, people moving faster than 10 miles per hour are traced in white. Those moving slower (likely by foot, bike, or driving through residential neighborhoods) are traced in blue:
That visualization begins to illustrate the difference between walkable parts of the city, and those places that are more likely accessed by car (or transit). Other recent research has shown that the characteristics of a neighborhood – whether it's walkable, whether it has a grocery store – are correlated with obesity. King County has no real food deserts. Everyone in the metropolitan area has some access to a full-service grocery store (96 percent of the people in this study also said that's where they do their primary shopping, not in smaller corner stores or bodegas). But learning about these other characteristics of a neighborhood may be relevant to better understanding why people choose the supermarkets they do and what kind of health outcomes they have.
The earlier Center for Public Health and Nutrition study, which included 2,000 respondents, found that people who shop in lower-cost supermarkets had obesity rates that were 10 times higher than people who shop in higher-cost supermarkets.
"Of course, it’s not Giant that’s making them obese," Aggarwal says. "We also have data on all the supermarkets in the area, and we saw that Giant carries the same things that Whole Foods carries. It's not that you won't find apples in Giant. It’s not that you won’t find vegetables in Giant." Although the brands and varieties may be different. "But still people are obese," Aggarwal says. "So it is something about the people who are shopping there, something about their attitudes, their economic barriers, their situations."
This means that once researchers better understand the real geography of where people access food, they may next be able to look into those very fine-grained individual decisions about why they go there and what they buy.
Above image via Schema Design.