For urban planners to do this, however, they first need to know what different parts of a city sound like. So the four researchers set out to create maps of a dozen global cities, including New York, Washington, London and Barcelona, that capture the full spectrum of urban sound.
To make these maps, the researchers didn’t wander around the city with a decibel meter. Instead, they analyzed large amounts of data from social media, stripping information about surrounding sounds from geotagged posts.
First, the researchers made what they call a “sound dictionary,” basically a list of all of the sounds that one might hear in a city, from crickets and coughing to farting and jackhammers. They separated these sounds into six categories: nature (such as thunder or the rustle of leaves); music (the sound of a guitar or the radio); indoor (the flushing of a toilet or the rustle of paper); transport (cars, helicopters); mechanical (drilling, alarms); and human (babies, footsteps, chatter).
Then they searched for these sound terms in social media, specifically by combing through millions of geotagged Flickr photos, so they could map up the sound tag with a specific city street. Finally, they used that data to create interactive maps of 12 cities around the world.
The map for New York City is below. You can see that Central Park and the areas along the rivers feature the green of nature sounds, but most of New York's city streets are drawn in blue, indicating that there is a lot of human noise. Across the river in New Jersey, you see much more noise from transport.
Here's what San Francisco looks like. In contrast to New York, there's a lot more green space with natural sounds, though some of the city's throughways suffer from traffic noise.
In an old city like Madrid, however, you can see that the noises of people and of music is predominant. Madrid's city center is so compact it discourages driving, so there is less noise from transportation.
You can see maps for more cities, including Washington, Miami, Seattle, London and Rome on the researchers' website -- just use the bar at the left to toggle through cities and sounds.
The researchers also used the tags to analyze and collect any clues about the emotions that people were feeling when they made the post. Their results suggest that streets with music sounds prompted more feelings of joy, sadness or melancholy, while those with human sounds like footsteps and conversation prompted joy and surprise. Traffic and mechanical sounds were more associated with anger and fear, while indoor sounds were associated with trust.
They then used this data to map what areas of each city are calm, exciting, chaotic or monotonous, as you can see in the map below for London. Unsurprisingly, parks are calming (green), while main roads are chaotic (red). Blue areas, which include some of the denser urban areas, are eventful or vibrant.