A method of creating map data is disclosed, the map data including a plurality of navigable segments representing segments of a navigable route in the area covered by the map with each segment being arranged to have speed data associated therewith. In at least one embodiment, the method includes processing speed data relating to a plurality of the segments of the navigable route covered by the map to generate a set of generated speed profiles, with each generated speed profile within the set being an approximation to traffic speed along one or more of the segments of the navigable route and each speed profile varying with respect to time; and associating at least one speed profile from the set with a navigable segment within the map data.