You may question what possible relevance this information has for you.
I would reply that I found myself agreeing to make not just one, but two scratch-and-sniff maps of New York City almost entirely by accident earlier this year. And even if you are more sensible than I am, and would never agree to such ill-informed adventures, it turns out that the magic of scratch-and-sniff map-making opens an entirely new perspective on the world -- an unexpected and invisible cartography of emotion, confusion and memory.
The first step, of course, is to decide what smells you are mapping. (The rest of the how-to comes a bit further down the page). Perhaps the earliest attempt to make an urban smell map dates back to Paris in the 1790s, when new ideas about both political equality and hygiene combined to send physician Jean-Noël Hallé on a six-mile odor-recording expedition along the banks of the Seine. His map-making technology consisted of nothing more than a notebook and pencil -- and, of course, his nose.
Today, artist Sissel Tolaas is the world's pre-eminent olfactory cartographer. She is midway through a survey of Kansas City, having already smell-mapped Paris, Vienna and Mexico City, with Nuuk and Calcutta next on her list. Although Tolaas still relies heavily on her nose, which she has spent years training, she also has a couple of important tools at her disposal, as she described her urban smell mapping process to me:
I try to go back to sites a couple of times to identify which smells remain over time and which change. If I have the time, I go back in different seasons and in different weather, so I can see which smells are important, underlying smells and how they change in different conditions. And I focus on finding the source for smells. If the source is definable and tangible, I can grab a sample and do a chemical analysis using a GCMS [a gas chromatograph/mass spectrometer] in my lab. If the source is not something that's portable, and if the budget allows, I will bring headspace technology into the field.
"Headspace" refers to a prohibitively expensive and utterly fascinating technology invented in the 1980s by Dr. Braja Mookherjee, a scientist at IFF, one of the world's largest fragrance and flavor companies. Mookherjee was obsessed with capturing the exact odor you experience when you put your nose up to, say, a living jasmine flower, rather than relying on an extract, or "absolute," as it's called in the perfumery business. In a paper (pdf) published in 1990 -- the same year IFF trademarked Mookherjee's discovery as "IFF Living Flower Technology" -- Mookherjee described his dissatisfaction with natural oils and extracts:
Before the extraction process, the fruits, flowers, and other plant parts must, of course, be picked. Very few people are aware of the fact that most fruits and flowers when picked soon exhibit a modified aroma from that of the living entity. This aroma continues to change with the process of decay. Hence, the oil obtained from the picked plant part does not replicate the aroma of the living material.
Sadly, Dr. Mookherjee passed away a few years ago, but Helen Murphy, IFF's Director of New Fragrance Development, explained how his process works to capture the odor your nose actually smells:
The idea is to capture, analyze, and then create the smell of nature. We use a special apparatus that captures the volatile components from the air surrounding the flower, fruit or plant. This is then analyzed in our R&D labs using a GCMS analytical machine that gives a fingerprint of the ingredients found in the flower. It is then possible to recreate this smell by putting together the different ingredients that were found in the analysis.
#1: Decide what smell information you want to map
Whether you use want to document and recreate the smelled reality of a city, like artist Sissel Tolaas, visualize a data set (for example, the geographical distribution of different types of fast-food outlets to regional variations in perfume popularity), or use your map to reconstruct historical or personal smell memories, you will need to gather your data and determine which chemicals or blends you are going to use. Depending on your map and budget, your tools at this stage can range from census data, market research, and scientific studies to headspace technology, a mass spectrometer, and your nose.
#2: Source and prepare your smells
Be prepared for difficulty and expense at this stage. Both chemical supply companies and fragrance and flavor houses will initially freak out at the idea that an individual (as opposed to a corporation the size of Kraft or Pepsi) might want to order their product. Even once you get over that hurdle, many of the ingredients you want will be unavailable, more expensive per ounce than gold, or only sold in five-gallon drums. If you need to mix or dilute smells, you will want to contact a scientific supply company or borrow a lab in order to pipette with any degree of accuracy.
#3: Micro-encapsulate your smells within a printable slurry
Although online information gives a reasonably clear idea of how this process works, I'd have to recommend not trying it at home unless you are an organic chemist for whom terms like "coacervation" and "partition co-efficients" hold no fear. Even the professionals at Arcade -- Anne Spratt and Gary Akins -- had a hard time making one of my smells (guaiacol, a smoky-smelling molecule present in the aroma of roasted coffee) "work" -- the capsule walls wouldn't stay intact until Akins added more diluent to the mix.
In order to create new raw ingredients for their perfumers and flavorists, Murphy told me that IFF has performed headspace analysis on an entire, specially planted botanical garden (above) full of fruit, flowers, herbs, and seeds. If her team finds an interesting or new smell, they can simply request a headspace analysis. "We have a huge library of these Livings," she said. "You don't have to limit it to flowers, obviously. We've used it to do things like the smell of a stone, the smell of mothers' milk, and even the smell of the skin of a virgin."
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.