Crowd Counting: Getting The Numbers Right

A few reliable methods

In the past it used to be difficult for journalists to estimate accurately the size of a large gathering. Often they have been caught in the middle between political opponents playing the numbers game. But modern methods make this tricky task a whole lot easier.

Recently protest marchers in Cape Town made history when they rallied the largest crowd ever recorded in South Africa.

Often when protesters gather in open spaces estimates about the size of the crowd fluctuate wildly to suit the whims of competing groups and interests. The count gets even trickier for political events, since opposing sides are keen to turn crowd estimates into ammunition for public relations purposes.

This proved to be the case for the march through the streets of Cape Town’s city centre to Parliament. Estimates ranged from 20 000 to 150 000. Inevitably those defending the Israeli government backed the lower figure while those supporting the Palestinian cause sought to boost support by inflating numbers.

“It’s very rare that you have the report of a crowd size where there isn’t some incentive to exaggerate one way or the other,” Dr Hannah Fry, a lecturer in the mathematics of cities at the University College of London, told the BBC.

Time Pressure

The BDS organisers put the crowd at 100 000. Time pressure does not always allow the journalist to mull over figures for too long. But as a professional, the journalist does have the responsibility to be as accurate as possible.

With the luxury of time and television footage, Richard Bosman, The City of Cape Town’s Executive Director of Safety and Security, has been able to deliver the most reliable estimate of the crowd.

After initially quoting a figure of 50 000 on the day of the march, Bosman has had a chance to get a more accurate count by using the city’s close circuit television or CCTV footage.

“We looked at the pictures after the march and judging by the distance between those at the front and those at the back, we estimated the length to be 2.5 km and then using a formula based on two people per square meter we worked out that there had to be between 75 000 to 80 000 people,” said Bosman.

That figure makes the August 9 protest nearly two and a half times larger than the historic anti-Apartheid march in September 1989 when an estimated 30 000 protesters marched through the city in defiance of the existing State of Emergency.

But the organisers went a step further and provided their own calculations. This diagram has been submitted in support of their claims.

A graphic depiction of the organisers' crowd calculations.

A graphic depiction of the organisers’ crowd calculations.

So how does a journalist go about estimating crowd attendances? Depending on the event, you could draw on information that is readily available. Crowds at a sporting event or a concert, for example, are simple to count because entry is controlled and people are counted as they pass through the gates or turnstiles. In a hall, one counts the chairs or at a stadium you could look up the capacity of the space before you do the story.

Estimating attendances at marches and rallies is trickier as the space is unregulated. Herbert Jacobs, a University of California journalism professor in the 1960s, devised a basic density rule that has been widely accepted.

Watching students protesting the Vietnam War from his office window, Jacobs saw they had gathered on a plaza that was arranged in a grid. He counted those in a few squares to get an average number per square and multiplied that by the total number of squares.

A Reliable Method

He also came up with a basic density rule that states a “light crowd” has one person per square meter and doubled that for a “dense crowd”. A “heavy crowd” would have as many as four people per square meter, according to this method.

Local authorities give permission for marches on the basis of exact routes. Newsrooms could establish before the time what the length of the route is and advise their reporters how many people would fill a kilometre of road. This would make it easier to estimate the crowd.

It is important to be as precise as possible because our stories are not just important for the moment or the day. It is important because it provides a historic record for all times.