For Those With a Stake, Crowd Size Does Matter

There is no question that last Saturday’s immigration march in downtown Los Angeles was massive.

But were there 500,000 protesters?

No one knows for sure.

The Los Angeles Police Department estimated the crowd at about half a million at its high point, after officers in a helicopter made a guess about the density of the crowd.

“It’s not an exact science,” said LAPD Lt. Paul Vernon. “They didn’t use any kind of grid system. It’s just an estimate.”

Organizers, meanwhile, insist that 1.3 million people attended, and they vowed to prove it.

Engineers volunteering their time have obtained aerial photographs of the march from Spanish-language television networks and are studying them, said Nativo Lopez, president of the Mexican American Political Assn. They should have results in a couple of weeks, he said.

It all underscores the fact that measuring the turnout at protests and other organized public events has become a controversial issue in recent years. Experts say there are scientific ways to gauge crowd size using complex grids, aerial photos, density ratios and flow analysis.

But most police agencies don’t employ such techniques. Neither the New York Police Department nor the Metropolitan Police Department in Washington, D.C, does crowd estimates.

Jeff Goodwin, a sociology professor at New York University who has studied crowds, said it would be difficult to get even a remotely accurate crowd count without taking aerial photos that could be broken into sections or grids for careful study.

Another method uses flow rates to estimate the number of people passing a specific point during a given period and then extrapolates over the duration of the event to arrive at a final figure.

The U.S. Park Police for years used a grid system for the Mall area in Washington, D.C. But the agency stopped doing crowd estimates after people challenged its conclusion that only 400,000 attended the Million Man March in 1995. Organizers in that case threatened to sue. A subsequent study by a Boston University professor placed the crowd at 878,587, give or take 25%.

In 2003, San Francisco police and organizers estimated that 200,000 attended an anti-Iraq-war protest. But when the San Francisco Chronicle had experts review aerial photos of the march, they concluded that only 65,000 participated.

Los Angeles officials said there was no doubt that Saturday’s march was huge, with crowds stretching down Broadway and Spring Street as far south as Adams Boulevard at times.

Capt. Andrew Smith said officers on the ground early in the protest placed the crowd at about 200,000. A few hours later, a chopper crew estimated it at about 500,000 at its peak.

“The estimate from last week I heard figured from 200,000 to half a million,” Police Chief William J. Bratton said, adding that Deputy Chief Michael Hillman said it was the largest crowd he had dealt with in 41 years. “As to the actual number, the human body takes up so many feet,” Bratton said.

Lopez, one of the march organizers, said engineers are doing a grid analysis of the aerial photos to determine how many people participated. He contended that police and the news media purposely underestimated the crowd count for political reasons.

Robin Ammon, a professor of crowd management at Slippery Rock University of Pennsylvania, said that even scientific studies -- using techniques based on a certain number of people per square foot -- still produce “pure guesstimation.”

This is because “a family could be standing very close together and, meanwhile, four to five people are taking up the same amount of space a few feet away,” he said.

Bratton said Los Angeles officials had expected a much smaller crowd and had prepared accordingly.

“Whether it was 200,000 or 500,000, they should be happy with it,” Bratton said, praising the peaceful nature of the protest. “We had an extraordinarily small number of police officers there.”

Brian Humphrey, spokesman for the Los Angeles Fire Department, said the most fascinating thing about the protest was not the size but the fact that no one was hurt.

But the Fire Department won’t be jumping into the fray on crowd estimates.

“We don’t want to touch that with an 11-foot pole,” said Humphrey.

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Times staff writer Kelly-Anne Suarez contributed to this report.