A system, for measuring a physical quantity representative of air quality in an observation zone, comprises a mapping with a set (V) of modeled values representative of the physical quantity; means for measuring the physical quantity and possessing N positions or N trajectories in the observation zone to exhibit a spatial distribution (Sopt); and means for calculating Sopt. The calculating means are configured to construct a mesh comprising G points in the observation zone; calculate, for a given spatial distribution, an estimator ({circumflex over (V)}) of the set V for each of the G points in the mesh; calculate a cost function representative of the difference or of the likelihood between {circumflex over (V)} and the V values extracted at the G points; and extract the Sopt to minimize or maximize the cost function.