A method of processing speed data is disclosed for use in the provision of enhanced map data including a plurality of navigable segments which together may define a navigable route in an area covered by a digital map. In at least one embodiment, the method includes (i) obtaining the speed data for at least one segment, the speed data including the measured speed of travel of a plurality of vehicles through the segment at different times; (ii) generating from the speed data for the at least one segment, data on at least one normal speed profile including an average speed of travel through the segment for a time recurring weekly; (iii) for at least one specified time, generating for the at least one segment data on at least one abnormal speed profile including an expected speed of travel through the segment during the specified time, the specified time being a time that does not occur weekly; and (iv) assigning to the at least one segment of the map data the corresponding normal speed profile and the abnormal speed profile for use by a navigation device in routing algorithms to determine a journey across the area.