Real-world examples of individual trajectories and collective movements. (a) Four examples of an individual trajectory from an empirical data set from mainland China and the corresponding collective movements. (b-d) Collective movements embedded in the data sets from the continental United States, Cote d'Ivoire and Belgium. Here the color bar represents the amount of mobility flux among locations per unit time, where a brighter (darker) line indicates a stronger (weaker) flux. Note that the spatial scales associated with these data sets are drastically different.