Standard OSM map of Nigeria by Computerteddy
This map of Nigeria is based on data from the OpenStreetMap Project. “Computerteddy” provides a worldfile “The Whole Earth In Your Hand" which consists of tiles sized 1ºx1ºas well as separate maps for Europe and for Germany. Some of his maps are routable which is nice, though they do not come with a Mapsource or a Roadtrip installer. The mapset is usually updated weekly.
OpenStreetMap works that way, that everybody can upload their GPS tracks from which maps from all over the world are being created. This means that the quality of the map depends on the tracks uploaded by the users (you're welcome to contribute to the project by uploading your tracks as well) and therefore the quality differs greatly from country to country, region to region and city to city. As there are continuously new tracks being contributed the maps are getting better and better every day, so if a map of a region is not as detailed as you had expected either join the community and help by contributing and/or come back in a few weeks or months and you will most likely find a better map with more data and information than there was before.