(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.