1. A system comprising: one or more processors; memory; a map segmentation module maintained in the memory and executable by the one or more processors to segment a map of an area into a set of sections; a function distribution module maintained in the memory and executable by the one or more processors to infer a distribution of functions for each section in the set of sections according to a topic model framework which uses mobility patterns of users leaving from and arriving at each section and uses points of interest (POIs) in each section; a section aggregation module maintained in the memory and executable by the one or more processors to group sections of the set of sections based at least in part on a similarity of the distribution of functions between each section to create functional groups; a functionality intensity estimator maintained in the memory and executable by the one or more processors to estimate a functionality intensity for each of the functional groups; and a group annotation module maintained in the memory and executable by the one or more processors to annotate each of the functional groups on a visual representation of the area.