1. A method for creating cost data for use in generating routes across an electronic map of navigable segments, the method comprising: receiving probe data from a plurality of users, the probe data comprising, for each user, movement data indicative of the movements of the user with respect to time, and physical exertion data indicative of at least one measure of physical exertion associated with the movements of the user over time; processing the received probe data for each user using an ability profile for the user to generate normalized routing cost data for one or more of the navigable segments of the electronic map; and associating the routing cost data with the one or more navigable segments of the electronic map.