What makes us feel safe on some streets and scared on others? Why is one neighbourhood nicer to live in than another? Which city looks better, Boston or Vienna? And why isn't there an app that just tells us how we work these things out?

When it comes down to it, we're not really sure how we make judgments on the quality of our surroundings – is it down to the architecture, the width of the street, the amount of greenery? Or are there other, subconscious factors at play on our perceptions? Does a street look nicer if there's a new Audi parked on it rather than a beat-up old Toyota? Perhaps we take in what people are wearing, the quality of the paving stones, the signage. It's often a matter of guesswork for architects and planners, too, when it comes to designing agreeable places and spaces. But the good news is: there IS now an app that can tell us this stuff. Sort of.

It's called Place Pulse, and it's more of an online experiment, run by researchers at MIT Media Lab, the Mecca of future-tech design. The experiment bit is very easy to participate in: you simply look at two street views and vote on which one has more "curb appeal".

At present, there are just three questions (which city looks safer/more unique/more upper-class?) and five cities (Boston, New York City, Linz, Salzburg and Vienna), so it's not exactly a comprehensive survey, but from the results published so far, we can at least answer the initial question. The perceived "safest" images are all from the Austrian cities, while the least safe are all in Boston. Why? You could characterise the safe places by tree-lined avenues, pedestrian areas and historic architecture. And conversely, the least safe places by empty expanses of concrete, unpopulated streets, conspicuous walls and barriers.

But what about those other, subconscious factors? The purpose of Place Pulse is not so much to come up with a league table of cities or areas, as to reveal the visual cues that make a place appear safer or wealthier. It's not gathering the data that counts – it's understanding it.

Place Pulse's software promises to analyse those crowdsourced votes (nearly 300,000 votes so far; the target is a million) and reveal the attributes that influenced them. This information will be presented as "a visual symphony of electronic data", the team promises. We'll have to wait for their exhibit at Linz's Ars Electronica festival in September to find out what the hell that means.

So how can this help the real world? One example is graffiti, says Place Pulse's Phil Salesses. City councils across the world spend millions cleaning up graffiti in the belief that it is universally undesirable, and yet in his home town of Boston there are safe, pleasant areas with plenty of graffiti. Rather than a blanket graffiti-removal policy, might that public money be better spent, say, cleaning soot off building facades, if that has a better net result?

Of course, there's a danger that this research could encourage cash-strapped city councils to simulate safe neighbourhoods rather than reduce actual crime rates. But anything that makes our cities a little less ugly is surely welcome. And a better-looking city could perhaps help reduce crime rates.

Place Pulse draws heavily on the work of Kevin A Lynch, an influential urban planner and former MIT professor. Lynch was interested in understanding the city not so much in terms of empirical data as people's mental images of it – how people navigate and read their environment. In effect, he told architects and planners that there was only so much they could do, but his work at least helped them to do it.

In the 21st century, there's a new layer to how we read a city: the electronic one. "Geo-social" devices such as smartphones, advanced mapping technologies and localised information are helping us to map places in novel ways. According to future-watchers, we're heading towards an era of "hyperlocality", when invisible webs of electronic information will define our environment as much as boring old trees and buildings. Having said that, you'd rather be hyperlocal in a tree-lined avenue than an abandoned parking lot, wouldn't you?