THANKS to Brett Goldstein, Chicago’s chief information officer, it is easy to discover a great deal about his city. In the past three months 5,973 vehicles were moved; since the start of 2011, 72,687 complaints about faulty lights in alleyways have been reported; and in the first half of 2012 the tourist-information website was apparently unavailable for 5,870 minutes. (The city says this was caused by a fault in the monitoring software.)

Needless to say, Mr Goldstein will want to get this fixed if he is to retain his annual salary of $154,992. Yet the nugget of data is a tiny detail in a vastly larger enterprise: to make Chicago’s data openly accessible and useful to the millions of people who live and work there.

Many cities around the country find themselves in a similar position: they are accumulating data faster than they know what to do with. One approach is to give them to the public. For example, San Francisco, New York, Philadelphia, Boston and Chicago are or soon will be sharing the grades that health inspectors give to restaurants with an online restaurant directory.

Another way of doing it is simply to publish the raw data and hope that others will figure out how to use them. This has been particularly successful in Chicago, where computer nerds have used open data to create many entirely new services. Applications are now available that show which streets have been cleared after a snowfall, what time a bus or train will arrive and how requests to fix potholes are progressing.

New York and Chicago are bringing together data from departments across their respective cities in order to improve decision-making. When a city holds a parade it can combine data on street closures, bus routes, weather patterns, rubbish trucks and emergency calls in real time.