Garmin Mapsource is good.
Garmin worldmap is... Basic. Better than a basemap (obviously), but only main roads and few minor roads are shown. The good news is Garmin do many many maps for individual countries which provide far more detail. Dont get these 2 confused by the way, Mapsource (MS) is the operating platform if you like, like fugawi, oziexplorer etc. Worldmap is just the overlay that runs in MS (appologies if this is teaching people to suck eggs).
The other good news is that there are many many maps from free sources/3rd parties that run on the garmin platform
people like Tracks for Africa T4A are just one example and offer some of the best routes throughout the African continent. Many more exist, its just a matter of searching.
As a planning and base tool, I dont think you could beat MS running on a laptop. Add in some free mapping or Garmins individual countries with papermap backup and you should be more than sufficiently covered.
Its all about covering all bases :coffeedrink:
G