1. A method of displaying road segments via an optical output device based on a map data base, which stores information on a road network in road vector data format, wherein a road segment is respectively represented by a vector, the method comprising: identifying a road segment for outputting via the optical output device; retrieving, from the map data base, information on a direction vector of the identified road segment and a parameter value associated with the identified road segment; selectively determining, based on the retrieved parameter value, a variation in shape of the identified road segment as a function of position along the direction vector; generating a graphical representation of the road segment for outputting via the optical output device based on the information on the direction vector and, if available, the determined variation in shape; determining, based on the map data base, whether the identified road segment has an end that does not allow vehicles to exit; and the retrieving the parameter value and the determining the variation in shape being selectively performed if the identified road segment has an end which does not allow vehicles to exit.