RoadMap is a program for Linux that displays street maps. The maps are
provided by the US Census Bureau, and thus only cover the US. 

RoadMap is at an early stage of development. At this time there are no
routing features implemented yet. RoadMap can only display the map around
a specified street address or follow a GPS device (using gpsd). The plan
for the future is to implement some navigation features similar to those
found in commercial street navigation systems. 

RoadMap uses a binary file format for representing the maps that is compact
enough to allow the storage of many maps on a Compact Flash or MultiMedia
card. The map of Los Angeles county takes about 10 Mbytes of flash space.
RoadMap comes with a set of tools to convert the US Census bureau data
into its own map format. 

WWW: http://www.geocities.com/pascal_f_martin/roadmap/