In order to bring more clarity to the crowd estimation process, Hotsheet asked Curt Westergard, the president of AirPhotosLive.com, to discuss his methods. Westergard's company has done aerial imaging for the U.S. border patrol, the Department of Homeland Security, companies building skyscrapers and cell phone companies trying to decide where to build their towers, among others.
"People hire us to get a really detailed view of what's on the ground," he said.
The company sometimes uses these images for crowd estimates, both generating its own estimates and partnering with Professor Stephen Doig of Arizona State University, a Pulitzer Prize winning journalist and crowd estimate expert, to come up with figures. For President Obama's inauguration last year, the company worked with Doig and GeoEye satellite data to generate a crowd estimate on behalf of CNN that was cited by the Associated Press and other news outlets.
To calculate attendance at the Beck rally, AirPhotosLive.com used what is called a surveillance aerostat balloon to take pictures from both above the event and closer to the ground. In the video above, which was provided by the company, you can see some of the images used to come up with a figure.
The balloon, Westergard said, gave the company the capacity to move up and down, allowing it to photograph people who were standing beneath trees in addition to taking photos from high above.
The company generated its own estimate and asked Doig to separately one on his own. Though Doig and AirPhotosLive.com employ slightly different methodologies, both use a method that involves laying grids over the high-resolution images and counting the density per unit of each grid cell.
Doig estimated that there were 80,000 people at the "Restoring Honor" rally, while AirPhotosLive.com estimated that there were 87,000 people, a statistically insignificant different since the margin of error was 9,000. CBS News elected to use the higher estimate.
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