For big-city dwellers, the idea of creating a catalog of the many aromas of urban life might seem like the project of a crazy person. For researcher Daniele Quercia, and artist and designer Kate McLean, it’s another way of seeing and assessing the concrete jungle.

Along with Rossano Schifanella and Luca Maria Aiello, the pair recently presented a paper at the 2015 International AAAI Conference on Web and Social Media examining the "smellscapes" of London and Barcelona. To collect the data, they took volunteers on “smellwalks” to identify the big wide world of odors in the cities—both pleasant and unpleasant.

Then they searched for the odor words (using their “smell dictionary”) associated with certain areas on geographically tagged social media. They looked at 17 million Flickr photos, 1.7 million tweets, and 436,000 Instagram photo captions posted from 2010 to 2014.

The resulting maps offer a new portrait of these oft-examined cities. The roads are colored in shades from red to green, with red indicating odors related to emissions and green indicating natural smells. As expected, areas around parks are heavily green, while heavily trafficked roads are red.

Aside from being fascinating visualizations of the olfactory experience, these maps can be used by urban planners to make cities kinder for pedestrians or help people find their most pleasant walking route, the researchers say. Emissions odors are often related to poor air quality, and tracking such data could be a powerful tool.

All this is to say, the next time you catch a breeze that makes your nose crinkle, start a mental index and consider a different perspective. It’s all just part of the aromatic map of the place you call home.