Understanding African ISP network topology is only possible with a thorough knowledge of where the OSI layer 1 is: specifically, where the submarine cables are, and where they are not. The cables that reached Accra, Ghana in the past ten years for transport capacity to London are a good example. And the more recent cables that connect Sierra Leone, Liberia ,etc.

https://en.wikipedia.org/wiki/EASSy

https://en.wikipedia.org/wiki/SAT-3/WASC

https://en.wikipedia.org/wiki/TEAMS_%28cable_system%29

https://en.wikipedia.org/wiki/SACS_%28cable_system%29

https://en.wikipedia.org/wiki/SEACOM_%28African_cable_system...

https://en.wikipedia.org/wiki/Main_One

https://en.wikipedia.org/wiki/ACE_%28cable_system%29

There is still a great deal of network traffic that takes a round-trip to Europe before reaching another African nation. As an example: If you look at the BGP adjacencies and IP space, all of the ISPs in Freetown, Sierra Leone are logically the same as if they were in a suburb of London.

Things are also heavily imbalanced in terms of the influence that .ZA wields. Something like 80% of the AFNIC IP space that is issued annually (in terms of cumulative number of newly issued ipv4 /24s) goes to .CO.ZA ISPs.