Estimating Crowd Size
POSTED BY || 27 March 2012

Iglesia ni Cristo (INC)’s Feb. 28 grand evangelical mission was in the news, in the airwaves and on the front pages. Speculations were rife that the activity, which took place in the Quirino Grandstand area of Manila’s Rizal Park, and was attended by thousands of devotees, was organized to support Chief Justice Renato Corona, who ‘s currently on trial in the Senate . INC officials insisted it was a purely religious event.

The media reports on how many INC devotees attended the religious activity varied widely. The count was anywhere from a low of 200,000 to a high of 2 million depending on which newspaper one read the next day.

Except for Bandila, the TV news programs that reported the event on the day it was held did not cite a specific figure.  They limited themselves to reporting that there were many people in attendance and that rally caused heavy traffic around the area.

The press, whether in the Philippines and elsewhere, has always stumbled when estimating crowd counts in large gatherings, although a number of articles have been written how to better provide crowd estimates.

UP Physics Professor Giovanni Tapang, wrote that the accepted method for estimating crowd size is “to measure the area covered by the protest and the crowd density, and then count the number of those who attended at a certain time.”

Herbert Jacobs, a professor at the University of California in the late 1960s, used the same method, which is easily done through overhead shots and aerial surveys. At the time he wrote the article, Tapang was chair of the scientists’ group Agham (Samahan ng Nagtataguyod ng Agham at Teknolohiya para sa Sambayanan) and an associate professor at the National Institute of Physics in UP Diliman. (“Measuring the size of crowds”)

“(Jacobs) developed a rule of thumb that is still being used in crowd estimation today. A crowd where each one is at arm’s length would cover about one square meter per person,” Tapang wrote.

Poynter Institute’s Al Tompkins, quoting an article, also wrote about Jacobs and several of his rules of thumb that are still being used today: “A loose crowd, one where each person is an arm’s length from the body of his or her nearest neighbors, needs 10 square feet per person. A more tightly packed crowd fills 4.5 square feet per person. A truly scary mob of mosh-pit density would get about 2.5 square feet per person.”

“The trick, then, is to accurately measure the square feet in the total area occupied by the crowd and divide it by the appropriate figure, depending on assessment of crowd density. Thanks to aerial photos or mapping applications like Google Earth, even outdoor areas can be readily measured these days.”

Other factors to consider are the uniformity of the crowd density, the timing of the estimate, among others, Tapang said in his article.

According to Tapang’s estimates, the Quirino Grandstand and Rizal Park (Luneta) can hold about half a million people. “The exposed area of the central quadrangle in front of the grandstand can hold up to 170,000 people. These estimates exclude covered areas, sidewalks and structures. Due to this limitation, these numbers are in the lower limit of the maximum capacity even if we use a density of four individuals per square meter.”

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