1. A system for monitoring the activity of objects comprising: a detector arranged to receive radiation from a scene; readout apparatus for monitoring and processing signals from the detector to identify objects meeting predetermined criteria appearing in the scene and to monitor the activity of identified objects within the scene; and data processing and storage apparatus; wherein: the data processing and storage apparatus is configured to compile statistical data over time indicating the occurrence of one or more object behaviours; and to determine the distribution of the one or more object behaviours over a contiguous area defining all or part of the scene.