Abstract ISO 15075:2003 specifies message content and format utilized by in-vehicle navigation systems. Its emphasis is on messages that are required to generate or enhance routing instructions. There is a particular focus on messages that would not necessarily be included in a more general traffic management message list. Although ISO 15075:2003 emphasizes requirements for Locally Determined Route Guidance (LDRG) systems that utilize on-vehicle map databases, it also includes messages that would be utilized primarily by Centrally Determined Route Guidance (CDRG) systems and certain value-added messages.