A trajectory determining device is designed for determining trajectory data (10) based on signaling data associating mobile communication device identifiers, time markers and signaling identifiers, at least some of the signaling identifiers designating a location cell. These trajectory data are used in order to identify pairs of movement markers associated with a same mobile communication device identifier, and corresponding signaling data, the time markers of which are between the time markers of a given pair, are reprocessed in order to return classified movement data (16) associating movement type data and departure and arrival data determined from location cells associated with the signaling data and a group of chosen locations.