Smell is notoriously subjective and hard to define. Odors can be perceived differently by different people depending on genetics, culture, past experience, the environment, and whether they've had a really bad sinus infection or not. Even worse, the same person can perceive the same smell differently at different times, depending on how the smell is described and other sensory fluctuations.

Leslie Vosshall's Laboratory of Neurogenetics and Behavior at Rockefeller University studies how complex behaviors are influenced by the chemical senses in organisms ranging from mosquitoes to humans. In order to better understand how human odor perception varies, both within individuals at different times and between different people, the lab asked nearly 400 New Yorkers to describe and rate the intensity and pleasantness of 66 different smells, at the same time collecting demographic data (significantly more diverse than the typical study of undergraduate psychology students) as well as data about their eating habits and perfume usage, finding many instances of variability in how people perceive smells. The lab recently published their extensive survey titled "An olfactory demography of a diverse metropolitan population" in the open-access journal BMC Neuroscience. They've also made their data freely available (you can download the huge excel file here) for further analysis or data-mining.

This study has been ongoing for several years, and two years ago inspired Nicola Twilley's wonderful Scratch-and-Sniff Map of New York's olfactory psychogeography. Rather than mapping what people smell, the odors that they would encounter in different neighborhoods, she mapped how they smell, mapping odor preferences by neighborhood using homemade scratch-and-sniff stickers, sampling some of the variation in our smell universe.

You can learn a lot more about the project from Edible Geography and from a detailed how-to in The Atlantic, as well as this video of a great talk Nicola gave about how we smell:

It's a lovely project, allowing people to explore the city in an unexpected way, using their fingers and noses to encounter the invisible. At the gallery opening, visitors also created their own crowd-sourced map by smelling the 12 different scratch-and-sniff options, choosing their favorite and placing it on their neighborhood on a blank map. For this version the visitors also were also asked to describe their favorite smell by writing on the sticker. The descriptions are remarkably poetic and the variation is striking. The same smell is described as "New England museum," "Altoid," "Relax," "Sunday June 23, 07:33am," and most surprisingly, "CAT LITTER." In the variation between preferences and descriptions, we see some of the way that odor can capture our imagination.