  Human mobility is becoming an accessible field of study thanks to the
progress and availability of tracking technologies as a common feature of smart
phones. We describe an example of a scalable experiment exploiting these
circumstances at a public, outdoor fair in Barcelona (Spain). Participants were
tracked while wandering through an open space with activity stands attracting
their attention. We develop a general modeling framework based on Langevin
Dynamics, which allows us to test the influence of two distinct types of
ingredients on mobility: reactive or context-dependent factors, modelled by
means of a force field generated by attraction points in a given spatial
configuration, and active or inherent factors, modelled from intrinsic movement
patterns of the subjects. The additive and constructive framework model
accounts for the observed features. Starting with the simplest model (purely
random walkers) as a reference, we progressively introduce different
ingredients such as persistence, memory, and perceptual landscape, aiming to
untangle active and reactive contributions and quantify their respective
relevance. The proposed approach may help in anticipating the spatial
distribution of citizens in alternative scenarios and in improving the design
of public events based on a facts-based approach.
