1. A computer implemented method of creating map data for a map, the map comprising a plurality of navigable segments, with each navigable segment having speed data associated therewith, wherein said speed data comprises a plurality of average speeds at which devices travelled along the segment represented by the navigable segment of the map, and wherein said speed data is grouped into a plurality of predetermined time periods over a period of time, the method comprising: processing the speed data to determine a measured speed profile for each of the plurality of navigable segments, said processing comprising averaging the average speeds within each of the plurality of time periods, such that the measured speed profile comprises a representation of the variation in traffic speed along the segment represented by the navigable segment of the map over the period of time; generating, based on the measured speed profiles, a set of generated speed profiles, the generating comprising processing the measured speed profiles using a clustering technique to identify similarities between the measured speed profiles, wherein each generated speed profile of the set of generated speed profiles is a representation of a variation in traffic speed over the period of time that is configured to be used to indicate a speed profile of any navigable segment having a sufficiently close measured speed profile; separately comparing the measured speed profile for each of the plurality of navigable segments to the set of generated speed profiles to determine which of the generated speed profiles is closest to that measured speed profile; associating, based on the comparing, one of the generated speed profiles from the set of generated speed profiles with each of the plurality of navigable segments; generating a map using the map data, such that the map comprises the set of generated speed profiles and, for each navigable segment, an identifier providing a reference to the associated one of the generated speed profiles; and providing, to a remote device, the map comprising the set of generated speed profiles and the identifiers for each navigable segment that indicate the associated one of the generated speed profiles.