O ct 2 01 4 A model of human population motion

We introduce a basic model for human mobility that accounts for the different dynamics arising from individuals embarking on short trips (and returning to their home locations) and individuals relocating to a new home. The two modes of motion occur on widely separated time scales and affect different phenomena: for example, short trips, constituting the bulk of human motion, dominate the spread of diseases, while the spread of genes or family names is more strongly affected by relocations. In many everyday life situations the two modes of motion need to be considered simultaneously. This is illustrated by a simple SIR model for epidemic spreading where trips and relocations lead to dramatic differences even under equal volumes of travel.