Estimate the Number of Protesters with SuperGIS Desktop

Scenario

On July 1st, 2014, Hong Kong residents marched through the streets to urge greater democracy in a rally. And a study commissioned by the South China Morning Post estimates 140,000 people took part in the march.

The result – calculated through computerized area-density analysis – is similar to separate estimates by two University of Hong Kong academics but falls way below the organizers’ figure of 510,000. The police did not offer a total but estimated the largest number of marchers at any one time at 98,600.

The number of people taking part in the annual rally has always been controversial, with police, the organizers and academics releasing widely different figures.

The dispute this year is further complicated by the slower-than-usual pace of the procession; it took a protester on average of three hours to march from Victoria Park to Central.

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Protesters take to the streets on July 1. Photo: David Wong
(resource: South China Morning Post)
Challenges

Limitations are acknowledged in the study for some marchers who joined or left the procession in the middle of the course may have been excluded for instance.

Goals

Since neither of the annual pro-democracy marcher’s organizer and the police offered an overall turnout, the Post commissioned chartered land surveyor Thomas Lee Wai-pang to provide an independent and alternative analysis. Lee and his team, Star Vision Limited (Supergeo Hong Kong reseller), used “the density and area computation” method that has been used by other media organizations to calculate crowd size.

Solutions

The surveyor utilized remote sensing to take aerial photos and applied GIS and spatial statistical tool subsequently to obtain the average density of the crowd in the sampled segments of the route.

Firstly, the surveyor applied SuperGIS Desktop and SuperGIS Spatial Statistical Analyst to display and estimate the number of protesters. SuperGIS Desktop integrates abundant GIS tools to offer GIS users from various domains a professional platform for geoprocessing, analyzing, displaying, editing,managing, and querying spatial data even faster and more easily. On SuperGIS Desktop, the aerial photos were adjusted precisely; and the spatial statistical analyst assisted the surveyor in estimating the number of protesters in each area. To calculate the number of marchers in the rally on July 1st, 2014, three Post reporters were assigned to the task. The first left Victoria Park at the head of the crowd at 3.25pm. He reached the finish point in Chater Road in Central at 6.20pm. The second reporter then left Victoria Park and arrived in Chater Road at 10pm. By then, the third reporter, who was at the tail of the procession, was in Wan Chai. This means between 6.20pm and 10pm, only half of the route was completely occupied. It may help surveyors to estimate the total number of protesters in the rally.

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Apply SuperGIS Deskotp to calculate the total area of rally
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Results

1. The total area of the rally route measured by utilization of SuperGIS Desktop (the Geographic Information System developed by Supergeo Technologies Inc.), to be 57,876 square meters.

2. The average density of the crowd was calculated by analyzing photos taken by Post photographers at three different locations throughout the event. The photographers took pictures of the crowd at a near vertical angle from 30 meters above ground at locations in Causeway Bay, Wan Chai and Admiralty.

3. By analyzing the photos with the satellite image analysis software, the average density of the crowd at the three locations at different times was able to be established.

4. By multiplying the average density with the total area of the route, the number of protesters filling the entire 4km route when the people at the front reached the end was calculated then.

Based on the density, Lee calculated that 91,213 people had taken part in the rally between 3.30pm and 6.30pm, and 49,195 between 6.30pm and 10pm. The two batches add up to 140,408.

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Effects:

With SuperGIS Desktop 3.2, the professional geographic information system, surveyors can apply the aerial photos taken by reportrs to work with the sampled segment of the route and assist the surveyor in obtaining the average density of the crowd and estimating the number of protesters in an objective and scientific way.

Resource: Ng, Joyce & Ng, Kang-chung (2014, Jul 3). SCMP study puts July 1 protest number at 140,000, well below organiser estimates, South China, Moring Post. http://www.scmp.com/news/hong-kong/article/1545694/protest-number-july-1-march-put-test

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