Police provided relatively low estimates and the protest organizers gave much higher numbers, both trying to prove a point.

For Reuters, this was an opportunity to provide an independent estimate that would be an indicator of political sentiment in one of the world’s premier financial hubs.

To do this, a team led by Deputy Head of Graphics Simon Scarr used Google Earth and TripAdvisor, fishing chairs and sunscreen, and pored over 18 hours of video to come up with an estimate of the size of the crowd in the streets.

Scarr first went through the three-km (two-mile) route of a march scheduled for July 1 step by step, spending hours on Google Earth to pin down locations where the bulk of the protesters would need to funnel through. These would be the places to monitor and measure the flow of the crowd.

“I spent time scouring the area for bridges and vantage points, looking down from them from all angles,” Scarr said. ”Eventually I was able to find a few elevated positions that would cover anyone marching to the government headquarters or end portion of the march.”

One of these vantage points was from a hotel. Scarr looked through traveler photographs taken from the hotel on TripAdvisor. Sure enough, one holiday maker shared a view of the city which incorporated the exact spot on the road the team needed.

Data Visualisation developer Marco Hernandez, based in Hong Kong, visited the sites and took test images and video.