I finally have a first prototype of what I want to show (in the first place) on my ipaq : my location (in the green part of EPFL) and the location of somebody for instance located in a car park (west part of epfl, in the upper left hand corner). Dots represent people's location.

At the moment, this map is a snapshot of a SVG file where Patrick and I mixed a jpg file (map of EPFL) and people's position (that we're going to get thanks to wifi antenna's position).