The Internet is now a very important medium for the acquisition and dissemination of spatial information. This importance results from the overwhelming popularity of the World Wide Web (WWW). In this process the map plays a key role. The map has multiple functions, such as that of its traditional role in providing insight into geospatial patterns and relations and maps can also act as an interface to other geospatial data. New cartographic challenges are raised in developing Web-based maps to provide visualisations of phenomena such as public transit systems. The authors explore the human cognitive processes involved in understanding transportation maps and using these maps for purposes of orientation and navigation in unfamiliar urban environments. Also addressed are the issues involved in designing 'Web-based' transportation maps and the limitations, opportunities and characteristics of the WWW to be taken into consideration by cartographers.