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 ?


What’s the documentary called?
Stealing this from OP, it’s called “Behind the Curve” and it is hilarious.
They do an experiment with a navigation unit from an airliner and it consistently proves them wrong too.