How big will inaugural crowd be? Do the math

Almost as soon as Barack Obama was declared the winner of the Nov. 4 election, projections of how many people will huddle on the Capitol Mall to witness his inauguration as the nation’s 44th president started inflating faster than the federal deficit. Would 1 million, 3 million or even 6 million (or one out of every 11 Americans who voted for him) join the throng?

And if you suspect those high-end projections are laughable, wait until you see the post-inaugural arm-wrestling and nay-saying from partisans and pundits over the dimensions of the "official" count.

When it comes to accurately counting crowds, the slogan should be "No, we can't." In reality, estimating the size of crowds at mass public events is much more about public relations than a quest for truth. Whether the crowd is gathering for an anti-war protest, a sports team's victory parade, a golf tournament, a pope's outdoor Mass or the swearing-in of the most powerful man on Earth, organizational reputations and personal egos are ballooned or deflated by public perceptions of whether the crowd is surprisingly large or disappointingly small.

Washington has been the site of many such examples of political popularity arithmetic, with inauguration crowds being only one example. Supposedly, George W. Bush drew 400,000 in 2005 and Bill Clinton 800,000 in 1993, compared to the record crowd of 1.2 million for Lyndon Johnson in 1965. "Supposedly" in all cases because no one knows for sure.

The most public brawl over the size of a big Washington crowd occurred in 1995, when Park Police estimated that 400,000 people had gathered for Louis Farrakhan's Million Man March. After Farrakhan threatened to sue, Congress banned the Park Police from making crowd estimates. Almost as bitterly disputed were the crowd estimates from a 2003 antiwar demonstration in Washington, which drew between 30,000 and 500,000 protesters, depending on who was doing the estimating.

A method for mob measurement
Even absent publicity-driven pressures to hype the size of a public gathering, no crowd that doesn't go through a turnstile can be counted without some margin of error. (And as recent election recounts have proved, even counting something as simple as a stack of ballots can have a considerable margin of error.) But some fairly simple math can be used to make defensible estimates of crowd sizes.

The method goes back to the late 1960s and a University of California at Berkeley journalism professor named Herbert Jacobs, whose office was in a tower that overlooked the plaza where students frequently gathered to protest the Vietnam War. The plaza was marked with regular grid lines, which allowed Jacobs to see how many grid squares were filled with students and how many students on average packed into each grid.

After gathering data on numerous demonstrations, Jacobs came up with some rules of thumb that still are used today by those serious about crowd estimation. 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.

Miami's annual Calle Ocho street festival, billed as "the world's largest block party", is a prime example of a claimed "million-plus" crowd that can be estimated better using Jacobs' method. Early on, the organizers of the 23-block event, which sprawls along the main artery of the city's Little Havana district, trapped themselves into annual increases on crowd size, so that each subsequent festival could be advertised as bigger and better than the last. Finally it became apparent that two-thirds of the population of South Florida would have to be dancing the merengue and eating croquetas shoulder-to-shoulder for the puffery to be true. So the Miami Herald measured the square footage of the festival area and calculated that it could hold a maximum of 175,000. Even if the entire crowd was replaced by new revelers at midday, it would be way short of what the organizers still insist on claiming.

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