For IFF's perfumers, the smell of a street corner in London is just another ingredient, to be combined and blended with other notes to make it more wearable, complex or beautiful. For Tolaas, that same smell is information that can be used to both navigate and understand the city. Rather than improvise upon odiferous reality, she creates a map built of smells, exactly as she found them.

But aspiring smell-mappers need not only document reality. Just like their non-odorous counterparts, smell maps can chart a layer of personal experience, history or social trends atop spatial reality. My maps, for example, which are now on display as part of the "You Are Here" exhibition at the Pratt Manhattan Gallery, sit side-by-side to compare New Yorkers' majority and individual smell preferences.

In other words, my scratch-and-sniff maps show how New Yorkers' smell, rather than what. To make them, I extrapolated data from the as-yet-unpublished results of an extensive study that tested the responses of four hundred New Yorkers to sixty-six different smells over a two-year period from March 2005. The experiment was conducted by Andreas Keller and Leslie B. Vosshall at the Laboratory of Neurogenetics and Behavior, The Rockefeller University.

"Our main goal was to try to find the difference between different variants in the DNA and different ways that people rank the smells on a seven-point scale from extremely unpleasant to extremely pleasant," Keller said. "We collected our subjects' demographic information just to control for those types of influences."

Nonetheless, that demographic information revealed some fascinating and significant differences in smell perception between men and women, young and old, and different ethnicities. For my map, I chose twelve of Vosshall and Keller's most interesting test smells, from complex natural extracts such as nutmeg and vanilla to single-note synthetic molecules such as octyl acetate, which is the basis for many artificial orange flavors as well as a key ingredient in Chanel No.5.

#4: Add a binder and apply the slurry Again, this is best left to the professionals. For scratch-and-sniff stickers, the slurry is pressed onto the artwork by a pad or roller and then blow-dried, as the final step on a flexographic printing press. Artist Sissel Tolaas has also developed formulae that can be painted onto fabric and walls. #5: Make the map Apply your stickers or paint in a way that best represents your geographic data. In my case, that involved attaching about a thousand circular stickers onto the wall using a projected map of New York City's community districts, as well as spreadsheets that combined census data with Leslie Vosshall and Andreas Keller's findings, in order to guide my placement. #6: Scratch! Then sniff! You can't "read" a scratch-and-sniff map without getting intimate. And while you're processing its geographic olfactory information, expect to gain a new awareness of your odor environment, trigger long-lost memories, discover unexpected smell prejudices, and even diagnose a previously unsuspected selective anosmia (the inability to smell certain molecules -- it's more common than you think).

Sourcing those chemicals was tough enough -- some, such as galaxolide, an artificial musk, were so jaw-droppingly expensive that I was lucky to secure a donation, while others only came in five-gallon barrels (I needed roughly a pound to make a thousand stickers), and all had to be shipped as hazardous material. Most came from chemical supplier Sigma Aldrich and IFF itself.