Method of processing positioning data

A method is disclosed, for processing positioning data to generate map data which includes 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 classifying the speed data associated with at least some, and generally each, navigable segment having speed data associated therewith into a category of a classification having a plurality of categories into which the speed data can be classified according to a parameter of a navigable segment with which the speed data is associated; generating a category average for each category within the classification; assessing at least some, and generally each, navigable segment within the map data to determine whether there is speed data associated therewith; and if there is no speed data associated with a navigable segment, using the category average, according to the parameter of the navigable segment being processed, as the speed data for the navigable segment being processed.