(click for larger version)

Eric Lormand of the Agenda did the counting and calculating, as he describes below:

My nice monitor, good eyes, spare hour, and distant memories of geometry

class say that in the peace sign there're 2500 people. I used the #1 photo

from Bob's site ... which will also be the combined front-and-back

ready-for-framing cover of Agenda, out this week ... and detailed photos

and the text of all the radical cheers in the centerfold--make sure you

learn them for next time!

Showing my work (or if you hate math you can skip what's between the dashed

lines):

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I reached three estimates from eyeballing the photo (a tilde (~) means

"closely approximates"):

(1) SPOKES: The lower right spoke ~ the average of the four spokes (it

mirrors the lower left spoke, and is midway in length between the longer

upward spoke and the shorter downward spoke). So call it "the average

spoke" and its length (excluding where it intersects the rim) "average

spoke length" and its average thickness "average spoke
thickness".

(2) RIM THICKNESS: The rim's average thickness ~ double average spoke

thickness, except for three areas (top, right, and stretched out along

lower left) where it ~ triple average spoke thickness instead. On average,

each of the three triple-thick rim areas ~ one average spoke length.

(3) RIM LENGTH: The rim ~ a circle with an average spoke as its radius (so

its length is pi times diameter, or pi times twice the average spoke length)

I then magnified the photo and one-by-one counted 125 people in the lower

right spoke.

By assumption (1), we can multiply 125 X 4 to get the total in the 4

spokes, 500 people.

By assumption (2), the rim ~ two complete circles of average spoke

thickness, plus three segments of average spoke thickness and average spoke

length ... in effect, two circles plus three spokes. The "three
spokes"

factor adds 125 X 3 = 375 people. For each of the two circles, we get pi x

twice 125 = 785 people, in each circle.

So we have 500 + 375 + 785 + 785 people, or 2445 people. You can easily

count another 50-60 people within the circle moving to and from the spokes,

so that's your 2500. That doesn't count the people on the grad library

steps and those still on their way from the march or on their way home.

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On Saturday in the diag I circled around the rim and did a rougher mix of

eyeballing, counting samples, and multiplying, and estimated 2800 people

total in the peace sign, on the steps and still arriving or leaving, erring

on the low side whenever there was doubt, so I could get a responsible

estimate for Agenda. My partner (Cecelia) did the same independently and

came up with 3000. We've long tried to cultivate our crowd estimating

skills and feel encouraged that they give results coherent with the more

controlled aerial photo calculations ... and more accurate than the UM

Daily and A2 News (fortunately) and Fox Detroit (unfortunately).

I recommend you adopt 2500 as a defensible and official count. Even with

all the time and magnification in the world, I don' t think the grain of

the photos would allow you to count heads much more precisely.

Last thing: assuming roughly there's 100,000 Ann Arborites and 10,000,000

New Yorkers (inflate their city pop'n to count their more extensive

commuter transportation and their desirability as a destination) and our

2500 is like a circle of 250,000 in Central Park.