How do people get a count for large gatherings such as the protest in Hong Kong, where it’s approximated that 2 million people are gathered

Question

How do people get a count for large gatherings such as the protest in Hong Kong, where it’s approximated that 2 million people are gathered

In: Mathematics

Answer 1

It’s a lot of estimating… someone will overlay a grid on a picture of the crowd. count several grids squares, get an average, then count the number of grid squares and there ya go… and decent estimate