  It is very important to understand urban mobility patterns because most trips
are concentrated in urban areas. In the paper, a new model is proposed to model
collective human mobility in urban areas. The model can be applied to predict
individual flows not only in intra-city but also in countries or a larger
range. Based on the model, it can be concluded that the exponential law of
distance distribution is attributed to decreasing exponentially of average
density of human travel demands. Since the distribution of human travel demands
only depends on urban planning, population distribution, regional functions and
so on, it illustrates that these inherent properties of cities are impetus to
drive collective human movements.
