1. Apparatus for generating supplementary information for a digital map, the supplementary information representing suitability of road use according to vehicle category, the apparatus comprising a processing resource configured to: (a) receive trip information representing sessions of logged journeys from a plurality of navigation devices, each session of a logged journey including vehicle category information in respect of a vehicle making the logged journey, (b) analyse the vehicle category information to identify at least one session corresponding to a vehicle category of interest, the vehicle category of interest including at least one selected from: a goods-vehicle; a bus; a car+caravan combination; a vehicle exceeding a predetermined weight threshold; a vehicle exceeding a predetermined width threshold; a vehicle exceeding a predetermined height threshold; a vehicle exceeding a predetermined length threshold; a vehicle carrying predetermined hazardous material; (c) analyse the trip information corresponding to at least one vehicle category of interest, to identify a route or route portion used by the vehicle on its journey; (d) analyse plural routes or route portions from a plurality of sessions to identify statistically at least one pattern of road use by the vehicle category of interest; and (e) generate said supplementary information based on the at least one pattern of road use by the vehicle category of interest.