Abstract: A computer implemented method for selecting at least one sensor from a plurality of sensors (130, 132, 134), wherein the at least one sensor is adapted to record sensor-data that is related to a geographical area (110, 112), wherein the sensor-data comprises information about objects (537) movable between locations (A, B, C, D, E, F) of that geographical area (110, 112), wherein a data structure (120, 121, 122, 123) with a pre-processed graph represents the geographical area (110, 112), the pre-processed graph having elements comprising nodes and edges, wherein nodes (a, b, c, d, e, f) represent the locations (A, B, C, D, E, F) of the geographical area (110, 112), wherein edges represent transition times (140) for the objects (537) if moving between the locations (A, B, C, D, E, F), and wherein the pre-processed graph has a simplified number of nodes (a, b, c, d, e, f) according to rules applied to the elements, the method comprising: receiving an event (135) indicator in relation to a particular location (B)