Monday, March 19, 2007

Iraq War Anniversary March - San Francisco, CA

After Sunday's rally, I was talking with friends who had also participated. They asked how large I thought the rally was. "Under 100,000..." (I was thinking about the size of a baseball stadium - something like that, maybe 60,000.) They thought the number was closer to 50,000.

(Just to establish some sense of scale for myself, I had briefly stepped outside the procession and stood by, roughly counting off the marchers in tens, as they passed. After a few minutes I had counted several hundred. I wasn't trying to be precise at the time. It was more of a habit - I often count things!)

Today, the “San Francisco Chronicle” reported "about 3,000" attended the march in San Francisco, and they went on to say the estimate was made by a reporter stationed along the parade route who counted people passing by. They admitted this number did not account for people approaching Civic Center Plaza from other routes, but the 3,000 number stood. I was incredulous. How could they be so far off the mark?

In an effort to test my own perceptions, and perhaps the credibility of event organizers, media and police, I spent several hours researching studies of crowd-size estimates. The first challenge to my perception was “well, what’s the capacity of a stadium?” The AT&T stadium (San Francisco Giants) is around 40,000. So, I could see my “yardstick” or point of reference was already off by 50%!

One of the most interesting studies was commissioned by the “San Francisco Chronicle”. It evaluated the size of the March 16, 2003 anti-war march and rally in San Francisco. Organizers and police had placed the number of participants at around 200,000. The “Chronicle” (perhaps in response to earlier challenges,) set out to scientifically estimate the crowd size. Using aerial photography taken at the peak of the event and applying a common analysis method (one I had used for estimating star field sizes in Astronomy), they concluded the crowd numbered about 65,000 (plus or minus 10%.)

In one frame, they showed what they identified as about 20,000 people in the Civic Center Plaza. I studied this aerial photo and tried to visualize how crowded the plaza was on Sunday, compared to this event in 2003. It was clearly less-crowded this weekend. But one-seventh as crowded? No. Maybe a quarter, maybe a third. Who knows.

What this little lesson did show is that my perception was off by an order of magnitude (10x)! This makes me wonder, of course, about numbers tossed around after the “March on Washington” (500,000?) If I had been thinking there were maybe 300,000 there, might the number have instead been 30,000?

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