Much of the land mass of Africa was shown on maps by the colour red. This meant that all such countries were part of the British Empire and many of them contained staging posts eg. airfields and lakes providing fuelling and maintenance facilities for both aircraft and flying boats linking the separate parts of the Empire as far afield as Australia and New Zealand.
The period would be around the 1920s and 30s. Imperial Airways was the name of the airline responsible for maintaining these extensive links so, your research could start with that name.