But to those building so-called “mobile” social networks, it is nirvana, linking virtual communities such as Facebook or MySpace with the real world. The idea is not new, but so far such services have not gained much traction. They have to be able to pinpoint people in order to work, but satellite positioning does not work indoors. More importantly, it is hard for such a service to gain critical mass: why join, if it does not already have many users?

A new generation of mobile social networks may have found ways to overcome these barriers. One is Aka-Aki, a start-up based in Berlin. Users of its service download a small program onto their mobile phone. The software then uses Bluetooth, the short-range radio technology built into many mobile phones, to check whether any friends or other members with similar interests are within 20m. If so, the program pulls down the person’s picture and whatever information he or she is willing to reveal from the firm’s website.

Where the economist gets all headmap.

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