Hi Alexandre
As far as RadarBox is concerned, it relies on each user of the system having their RadarBox switched on and connected to the internet. They can then send details of all the ADS-B equipped aircraft in their vicinity to the RB server for sharing with all the other users.
So, first there have to be RB users in the area, and second, there have to be ADS-B aircraft around. At the moment, unfortunately, there are very few users in Africa, and very few ADS-B aircraft for them to pick up.
As Marc has said before, even though he's got both, his use of the internet is very expensive, so he's not connected most of the time, so we can't see his data (and he can't see ours).
There are more people buying RB all the time, more and more aircraft are being fitted with the equipment, and internet access for most people is getting easier and cheaper, so it's constantly improving.
Hope that helps.
Rod