“VIBRANT” is a word often used in guide books to describe a particular quarter of a city: Soho, in London, for example. But what does that actually mean? To Daniele Quercia of Bell Labs in Cambridge, England, and his colleagues, the term has a literal truth to it. Soho is a place of good vibrations through the air—good sounds, in other words. It shares this with the Gothic quarter of Barcelona, for example, but not with much of Mayfair and Belgravia, upmarket London districts near Soho that Dr Quercia brands sonically “chaotic”.

He and his colleagues, who report their results in Royal Society Open Science this week, have been making sound maps of the two cities. In so far as city planners incorporate matters sonic into their thinking, Dr Quercia notes, they take most notice of noise. This form of sound, being by definition annoying, has political resonance, and planners do their best to minimise it. But sound can also be soothing, exhilarating, saddening, surprising and many other things besides. These aspects of the urban soundscape are little-studied. Dr Quercia thinks this is a pity. The spread of information technology, and in particular of social media, has created a pool of data about urban sounds that can be tagged to precise locations. That has let him and his team start correcting the omission.

Using a statistical analysis of people’s reactions to different sorts of urban sound, the team drew up four broad categories: chaotic, calm, monotonous and vibrant. Mechanical sounds tended to be chaotic. Human ones tended to be vibrant. The sounds of nature, though, could be either calm or monotonous. Birds chirping were calming. Crickets chirping were monotonous. Rain pattering down from the sky was monotonous, but dripping from trees it was calming. Drawing on social media to show which sounds people report hearing around them in particular places, the team then mapped the centres of the two cities accordingly.

Not surprisingly, parks, such as Hyde Park, sound calm. More surprisingly beaches (at least, those in Barcelona) are monotonous. But, main roads aside (they are usually chaotic), a stranger to either city would have difficulty predicting from a map which streets would have good vibes and which would seem chaotic. That would bear further investigation, and perhaps even the attention of forward-thinking planning departments.