The research team employed remote sensing to capture aerial imagery of the procession and deployed GIS and spatial statistical tool to get the average density of the crowd in three sampled segments of the route. The crowd images were captured at a near vertical angle from 30 metres above ground at three locations in Wan Chai, Causeway Bay and Admiralty.
The total calculated area of 57,876 square meters of the rally route was multiplied with the average density of the crowd in three locations while considering the average time taken to complete the rally route. The resultant calculations estimated the number of protestors to be 140,408, which turn out to be higher than the police-submitted figure of 98,600 and significantly lower than the figure of 510,000 as claimed by the event organizers.
The SCMP did acknowledge some limitations in the study. Some marchers who joined or left the procession in the middle of the course may have been excluded for instance.
Source: South China Morning Post