Crowd counting is a technique used to count or estimate the number of people in a crowd. At ticketed events, turnstiles are often used to precisely count the number of people entering a venue. At unticketed events, especially events that take place in the streets or a park rather than an enclosed venue, crowd counting is more difficult and less precise. For many events, especially political rallies or protests, the number of people in a crowd carries political significance and count results are controversial. For instance, the global protests against the Iraq war saw many protests at which widely differing counts were offered by organizers on one side and the police on the other. Another memorable incident occurred when Louis Farrakhan threatened to sue the Washington, D.C. Park Police for announcing that only 400,000 people attended the 1995 Million Man March he organized.
The most common technique for counting crowds at protests and rallies is Jacobs's Method, named for its inventor, Herbert Jacobs. Jacobs method involves dividing the area occupied by a crowd into sections, determining an average number of people in each section, and multiplying by the number of sections occupied. According to a report by Life's Little Mysteries, technologies sometimes used to assist such estimations include "lasers, satellites, aerial photography, 3-D grid systems, recorded video footage and surveillance balloons, usually tethered several blocks around an event's location and flying 400 to 800 feet (120 to 240 meters) overhead."
Simple Methods using geometrical shapes of the area
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For example, if a park is 2,000 ft long and 600 ft wide, the area of the park is 1,200,000 sq.ft. Average person needs at least 2 sq.ft of space to stand close body-body in a crowd. So this park can accommodate 600,000 people when fully occupied. Now if people are thinly stretched, then it would be little difficult to estimate. Still we can on rely aerial surveys as how thin or how dense people are in the park. Then use the area to estimate the crowd.
Now, if it is a downtown area rally where people are standing on either side of streets behind the barricades - that is easy to estimate. For e.g say , if the side walks is 20 ft wide and people are lined up to 2miles then a 20ft side walk allows people to stand 20 deep (20 people in a column). The estimated area will be 20ft x 1mile in ft x 2 (2 for both sides of the street). So 20 x 5280 x 2 = 211,200. Again assuming a person needs an average space of 2 sq.ft standing body-body (but not touching each other) state the crowd in this case would be 211,200/2= 105,600 people. Unfortunately, it usually depends on who is counting. Pro-rally individuals may exaggerate and anti-rally individuals may understate.
- Melina, Remy (September 3, 2010). "How Is Crowd Size Estimated?". Life'sLittleMysteries.com.