The two trans-Africa routes were of interest to me...
Trans-Saharan DownThe Trans-Saharan Highway is one of the oldest transnational highways and the most complete. Can however be rough to get through the middle of the Sahara.
If you want more, continue from Lagos down to Namibia or even South Africa.
Cairo - Cape TownThe Cairo - Cape Town Highway will take you most of the way, but a little detour to Namibia towards the end might be worth it. Some parts of the road is unpaved, giving a rougher journey.
Be prepared with visas and papers for all the border-crossings, as well as local conflicts.
Overall, the map is a good start in highlighting the major overland routes however the descriptions of each route need slight amending. "...rough to get through the middle of the Sahara" is a bit of an underestimate. This route has been closed for decades (unfortunately) but credit is due to the author as this route is certainly one of the most interesting. A few books and blogs detail the transit across the Sahara in detail that leaves one yearning to experience.
The Cairo to Cape Town is by far the most popular route with the least visa issues (compared to West Africa) and can mostly be done on paved roads. The author mentions local conflicts but these hardly affect overlanders.
Africa has a few overland routes - read more about choosing an overland route and one of the lost routes from West to East Africa.