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Why it’s usually difficult for people to agree on a crowd’s size

From US President Donald Trump’s January 20 inauguration to Hong Kong’s 2014 Occupy Movement protests, reporting accurate crowd numbers has always been difficult, with aerial image analysis regarded the most accurate

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Pro-democracy supporters gather at Admiralty on October 10, 2014. Photo: AFP

If there is one fact that everyone can agree upon about the size of the crowd during US President Trump’s inauguration, it’s that an inordinate amount of time was spent arguing about it.

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Short of individually counting attendees one by one – and barring technological advancements that could retroactively analyse images to do so – there may never be undisputed numbers pinned to the inauguration or the Women’s March on the US capital the following day.

It’s an argument we are all too familiar with in Hong Kong, estimates of attendance numbers given by rally organisers and police consistently differ widely.

The Hong Kong Alliance in Support of Patriotic Democratic Movements in China, which organises the annual June 4 vigil to commemorate the 1989 Tiananmen Square crackdown, said 125,000 people attended last year’s anniversary. Police put the figure at a mere 21,800.

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A month later, the Civil Human Rights Front, which organises the July 1 protest march to mark the return of Hong Kong to China, put the attendance number at 110,000. Police counted 19,300 protesters at the peak of the rally.

In 2014, the South China Morning Post commissioned an independent computerised area-density analysis of the July 1 march. Land surveyor Thomas Lee Wai-pang measured the total area of the route at 57,876 square metres, and calculated the average crowd density by using photos taken at various locations by Post photographers. He arrived at a figure of 140,000 protesters. This contrasted with both the organisers’ optimistic number of 510,000 and the conservative police estimate of 98,600.
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