How to size up the crowd - a lesson in Cairo

CAIRO/WASHINGTON - Just how many protesters are there in Cairo’s Tahrir square? Media accounts vary enormously. The crowd estimates depend on rough calculations, including one developed by a former reporter about 45 years ago.

Assessing crowd strength, even in this age of satellite imagery, continues to be a rough science. This was evident during demonstrations at Tahrir square where news accounts put the figures anywhere from tens of thousands to two million.

“If two million people show up that means a significant plurality not only wants Hosni Mubarak to step down (as president) but is stepping out on the streets to say it,” Wall Street Journal quoted Ben West, a tactical analyst with US intelligence firm Stratfor, as saying.

Protests are continuing in Egypt to seek the ouster of President Mubarak. The protesters have gathered at Tahrir square, making it the centre of the unrest that has swept the country.

Analysts feel that Tahrir Square cannot hold two million people — or even any more than 250,000.

The numbers were calculated by combining the area of the square with an old rule of thumb that in a very tightly packed crowd, each person would occupy 2.5 square feet.

The media report said the estimates are of capacity and they don’t mention whether the square was completely filled or to how many people came and went throughout the day.

To arrive at detailed assessments would need wide-angle overhead photos or satellite imagery, and several of the world’s major satellite-imaging companies don’t have snapshots of the Cairo protests at their peak levels this week.

West used satellite images to estimate the size of Tahrir Square, which is actually a space with fuzzy boundaries more closely resembling a traffic circle than an actual square, at 490,000 square feet.

Thereafter, he used the calculation of the 2.5-square-foot per-person estimate to arrive at the capacity of about 250,000 people.

It is, however, onetime newspaper reporter Herbert A. Jacobs who is credited with developing a method to count crowds.

Jacobs lectured at the University of California during the tumultuous 1960s and wondered how many students were participating in protests there against the Vietnam war.

He initially figured that one person was occupying around four square feet in the densest crowds. Later crowd researchers brought down the figure to 2.5 square feet per person.

The Wall Street Journal said that since there were no skyscrapers closeby and no helicopters buzzing overhead the Tahrir Square protesters, the only reliable way to measure the crowd was through satellite images.

However, satellite images often won’t work when it is cloudy, as it was on Friday.

Without aerial photographs, counting crowds is largely guesswork, the media report said, adding it wasn’t clear where some of the Cairo numbers originated.

The latest technique is to have computer scanning of multiple high-resolution images of many parts of a crowd if density varies.

A benchmark for protests is Beijing’s 1989 Tiananmen Square.

“Chinese and foreign reporters estimated about a million people were on the streets,” Scott Simmie and Bob Nixon wrote in a 1989 book about the Beijing protest. “But how does one count a million?”