“An amazing 1 million people are estimated to be marching today at the #PutItToThePeopleMarch,”
People’s Vote UK, 23 March 2019.
Last Saturday, protestors marched in London to call for a ‘People’s Vote’ on the final Brexit Deal. The organisers claimed that 1 million people marched, and that figure was repeated by a number of news outlets. We’ve been asked by readers to check this claim.
The reality is that it’s hard to precisely measure crowd sizes at non-ticketed events. That said, experts in crowd estimation have said the crowd on Saturday was less than half the size estimated by its organisers.
Talking to Wired magazine, Manchester Metropolitan University’s Professor Keith Still, said “based on the visuals from the helicopter image, it’s between 312,000 and 400,000 people.”
This type of crowd estimation, called the Jacobs method, is done by dividing a crowd site area into sections, measuring the size of each section and then multiplying each area by the estimated density of people within that subsection.
How did the People’s Vote estimate 1 million?
The People’s Vote said they estimated the size of the crowd using information from staff and volunteers as well as examining aerial pictures from helicopters.
They said that “peak crowd densities were estimated at 4.5 people per square metre”. (For context: Professor Still says the average crowd has between two and four people standing per square metre, and anything more than four people per square metre becomes too uncomfortable to move).
But even if this density of 4.5 people per square metre (visualised below) had been observed across the whole march site of roughly 160,000 square metres, that would only account for 700,000 people.
Helicopter footage shows there were areas where the crowd was much less dense than 4.5 people per square metre.
We also wrote about this issue in October last year, regarding a previous People’s Vote march, when we also believed the march organisers had likely overestimated attendance.
In addition to the organisers’ estimate, there were rumours circulating on social media that claimed the Metropolitan Police had estimated that 2 million people attended the march on Saturday.
The Metropolitan Police told us: “We do not confirm crowd figures for marches or protests.
“This is a matter for the event organisers.”