Just a thought experiment, let’s say the earth is flat, looks like many professionals would know, including
- 
Pilots/ATC/sea captain 
- 
Land surveyor and civil engineers 
- 
Astronomers and Geologists, at least the one dealing with experimental data 
- 
Militaries, at least radar operator and artillery 
Just these categories are already a lot of persons, I assume I miss a lot of others. So how many person does it make in total ? 10 % of the population ?


One of the best Star Trek episodes ever: https://en.m.wikipedia.org/wiki/Chain_of_Command_(Star_Trek:_The_Next_Generation)