Inauguration Crowd Count

Barack Obama became the 44th President of the United States last Tuesday, January 20th at precisely 12:00 PM ET. Many converged on the National Mall for this historic occasion, but exactly how many made this historic trek? Thanks to satellite imagery, provided by GeoEye, an accurate estimate of attendance, or at least area, can be ascertained.

I downloaded the high-resolution satellite image and traced the population areas in Adobe Acrobat. Using the resulting polygons, the area can be calculated:

(Click the image for a larger version)

The Inauguration Crowd Size Covered 2,230,000 Square Feet

The effective scale is acquired by measuring the diameter of the Washington Monument's base (which we know to be 250 feet) on the image, and converting to real world measurements. In this case, each inch represents 500 feet. A table of each polygon's area is listed below:

       Label    Area (sq ft)   Label   Area (sq ft)
         0        132,500        19       15,000
         1         20,000        20       25,000
         2         27,500        21      105,000
         3        302,500        22       10,000
         4         5,000        23       52,500
         5        287,500        24      100,000
         6         12,500        25       27,500
         7         72,500        26      125,000
         8        117,500        27       65,000
         9         12,500        28       75,00
         10        25,000        29       75,00
         11       155,000        30       7,500
         12        40,000        31       57,500
         13       172,500        32       27,500
         14        27,500        33       17,500
         15        27,500        34       7,500
         16        45,000        35       32,500
         17        32,500        36       20,000
         18       140,000      Total    2,365,000

Despite their appearance, these figures are not exact. The area calculations are quantized based upon the capabilities of Adobe Acrobat and the resolution of the image. It would have been better to use a tool like AutoCad to trace the regions, but even so, the resolution issue would still persist. The resolution of the image makes it impossible to accurately trace each and every crowd region. Based upon these assertions, and the knowledge that low-density crowds are not visible to a satellite, we know that some spectators were not and cannot be identified; their exact number will forever remain unknown. It then follows that our 2,365,000 sq. ft. figure excludes these spectators.

While we have a baseline measurement for the size of the crowd, we still do not know the quantity of the crowd. Fear not, our Clinton Era tax dollars were hard at work:

In the model, all people are modeled in circles individually to consider human spatial requirement. The diameter of a circle is determined as 0.4 meter with consideration of the size of body. Using the distance between evacuees and spatial requirements, interactions between people are assessed. It is an important factor in predicting congestion or contra-flows of a crowd.

Source: Building and Fire Research Laboratory via

The area within a circle of diameter .4 m is 0.125 sq. meters; this then converts to a crowd density of one person per 1.35 square feet. If this density is uniformly applied to our baseline area of 2,365,000 ft. sq, we can obtain a minimum boundary for the number of inauguration onlookers; at least 1,748,445 people attended Barack Obama's Inauguration.

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13 Response(s) to Inauguration Crowd Count

1/25/2009 2:28:39 PM CT

They look like ants to me.... :o)
1/25/2009 2:32:38 PM CT

Man, do you need to get a life...
quadratic relationship
1/25/2009 3:01:16 PM CT

40 cm is not really that big... and the assumption is these people would have to be standing literally in physical contact with each other. A small change in the diameter assumption dramatically affects your estimate. For example, if the area was based on 50 cm, you lose hundreds of thousands of people.
1/25/2009 5:33:18 PM CT

Does this take into account that Americans are fatter than 0.4m diameter ?
1/25/2009 6:29:29 PM CT

And also, there where many people in the surrounding building balcony and roofs who could not be seen from the satellite view. Who knows how many were really there?
1/25/2009 7:29:34 PM CT

many people have said that the geoeye image is not the one taken at 12. if you look at the gigapan image ( ) you will see the actual innauguration had many more people than the geoeye pic. Also the washington monument makes a great sundial.
1/25/2009 8:01:27 PM CT

In doing a simple calculation using 2,365,000 sf (the area of spectators on the satellite image) divided by 1.35 square feet (the area of a circle .4m in diameter) you are completely leaving out the space between the 'circles'.

Your calculation is a good first start, but faulty logic has been applied in arriving at the 1,748,445 figure.

Think of a case of beer - the 12 round objects are placed within a rectangle that has space between the cans because the circles touch each other at their midpoints. You haven't accounted for the area between the circles.
1/26/2009 12:53:41 AM CT

I doubt that an *average* person with heavy winter clothing fits into an an area of 1.35 square feet.

For example, my shoes (almost exactly 12" long) alone don't fit into an area of 1 square foot when I'm standing naturally. What about my shoulders? What about some space between people for comfort?

The correct number is probably closer to 4 to 5 sq ft per person, perhaps more.

I propose that you look around the web for the standard crowd packing for an American (slightly overweight) crowd dressed in winter clothing.
1/26/2009 4:33:29 AM CT

40cm equates to a waist size of 50 inches in the imperial measure. As an average, that's probably pretty close, considering children, younger/fitter attendees, and the under-representedness of the stereotypical couch potato in outdoor events.

Remember that the purpose of the research cited was to find a crowd-packing coefficient. I'm happy to trust the figure, and it accords with other estimates I have read.
1/27/2009 7:27:35 AM CT

the gigapan proves nothing about size of the crowd relative to what is depicted in the image on this page-it shows too small an area
*except* it does seem to jive with the one on this page
1/27/2009 9:33:37 AM CT

I was there and I can tell you we were pretty much standing on top of each other. It was near impossible to pivot your shoulders or stick your arm above your head if it was by your side.
1/27/2009 3:20:13 PM CT

Maybe someone should try using GIS software to get the answer...
1/27/2009 3:43:00 PM CT

most estimates of crowd size use 4 square feet for a 'dense crowd' and 5 - 10 square feet for a 'loose crowd' (Herbert Jacobs, Journalism proffesor at Berkely did some research on the subject to better understand Vietnam War Protests, and established these rules of thumb.) Assuming a crowd density of 1 individual per 3 square feet (a very dense crowd) the photo above would seem to indicate a crowd of about 780,000. It is also interesting to compare the crowds photographed for the 'million man march' in 1995, which was estimated at somewhere between 400,000 and 1 million people. that march was held on the same location, and appeared to fill a significantly larger portion of the mall than is filled in the photo above. The question about the time of day of the above photo is an interesting one... although I suppose someone could use the shadow of the Washington Monument to make a good estimate if they were so inclined...

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