In the context of the European Project CarTalk 2000, a mobile ad-hoc network composed of vehicles will be developed to improve the safety and comfort of driving. The highly dynamic topology of this network brings up a number of new challenges, e.g. packet routing. This thesis introduces a new geographic forwarding approach that is based on the spatial model information about the environment (e.g. extracted from digital maps of a car navigation system). The protocol developed in this thesis is called "Map-based Geographic Forwarding" (MGF), which uses the available spatial model information to optimize local geographic forwarding decisions. The conceptional design of MGF is evaluated in ns-2 and compared with the existing geographic forwarding approach GPSR.