Location-based audio file in Marseille

Tag for location-based information A subtle cue on the pavement that indicate that you should press "2" on the audio-guide. An interesting location-based service which do not necessitate a GPS or any other positioning technology. In this case, it relies on people's curiosity and will to spot this sort of red dot on the pavement.

Why do I blog this? apart from the general aesthetic of the cue, it's interesting to contrast this sort of approach and a positioning technique. What are the pluses and minuses? What are the conditions under which it would be better to let people spot such cues (and hence be more active)?