The Canada Transportation Base Map (CBMT) web map service of the Earth Sciences Sector at Natural Resources Canada, is an Internet service which is intended primarily for online map application users and developers. This service is compatible with OpenGIS® Consortium (OGC) (http://www.opengeospatial.org/) Web Map Service (WMS) standards and specifications, version 1.1.1. This base map service has been created to provide locational context with an emphasis on transportation networks over which thematic information can be overlaid. Cartography (colour, symbology, etc.) of the base map has been specifically designed so that thematic information will be more prominent than the locational context information. The range of viewing scales for this service is between 1:60,000,000 and 1:10,000. Features from the following data sets are used by the CBMT service: CanVec, GeoBase, the National Topographic Data Base and base data from the Atlas of Canada National Scale datasets.