1. A computer-implemented method of creating map data for enhancing a digital map comprising a plurality of navigable segments representing a network of navigable segments, the method comprising: applying point locations to the map which correspond to individual events on the network; generating a heat map representing the concentrations of events according to a selected distribution function; applying a threshold calculation to the heat map to identify one or more zones on the network having a high concentration of events; associating the or each zone with at least one segment in the digital map; and providing a warning based on the identified one or more zones.