  Human mobility is investigated using a continuum approach that allows to
calculate the probability to observe a trip to anyarbitrary region, and the
fluxes between any two regions. The considered description offers a general and
unified framework, in which previously proposed mobility models like the
gravity model, the intervening opportunities model, and the recently introduced
radiation model are naturally resulting as special cases. A new form of
radiation model is derived and its validity is investigated using observational
data offered by commuting trips obtained from the United States census data
set, and the mobility fluxesextracted from mobile phone data collected in a
western European country. The new modeling paradigm offered by this description
suggests that the complex topological features observed in large mobility and
transportation networks may be the result of a simple stochastic process taking
place on an inhomogeneous landscape.
