Transit maps are topological maps, usually in the form of schematic diagrams. They illustrate the routes and the stations within a public transport network, usually tramways, bus lines, subway/metro lines or ferries. The diagrams are color coded lines to indicate each line, with named icons to indicate stations or stops. A transit map is usually found at the platforms, in printed timetables or in the transit vehicles themselves. Their main function is to help users to efficiently use the public transport system, including which stations to use as interchange between lines.