Johannesburg just barely misses the list at a little over 5.6 million. The reason it may seem low to Jetpunkers is that this source goes by metro area instead of urban area like the numbers we are used to. Although 5.6 million is a possible number for 2100, I believe the number will be higher at that time looking at other predictions. The point of these quizzes is not to give an exactly accurate number, just to get an idea of what populations can look like 80 years in the future.