On-the-ground estimates of crowds are notoriously unreliable, say crowd counters like Clark McPhail, emeritus professor of sociology at the University of Illinois at Urbana-Champaign. Instead, aerial photos capture the true density of a crowd, which can be calculated by factoring in the dimensions of the space in which people are gathering.
To count how many people attended the Sunoco Red Cross Pennsylvania 500 at Pocono Raceway on Aug. 1, the Pocono Record took 110 aerial photographs from a height of 3,000 feet with a telephoto lens at the start of the race.
The entire raceway was photographed for context, as were swaths of each section of the grandstands and the infield. The clearest 38 photographs were selected, with substantial overlap from one image to the next to ensure there were no major gaps.
Seven photographs of the grandstands were blown up on computers, with spectators counted in each seat or bleacher and measured against the seating capacity that reporters gauged before the race.
Another 31 images covered the infield, but only cars and recreational vehicles could be seen from the sky. The Record counted about 2,325 cars and 1,145 RVs, and estimated, on average, that three people fit in each car and five in each RV, then multiplied.
The count of the bleachers and infield yielded an initial result of about 41,700.
To account for error, people milling out of sight in the bathrooms or concession stands, or coming in late after the rain delay, we rounded up, adding a 15 percent margin of error. This brought our adjusted total to 48,000 — less than half the 100,000 announced by NASCAR.
To make sure that we weren't counting unfairly by basing our figures on the start of the race, we compared our aerial shots with those taken from the ground later in the day. Those images show the stands to be similarly crowded — or uncrowded.
Try about half that number, according to an independent count by the Pocono Record.
Attendance figures at the track long have been closely guarded by Pocono Raceway — though NASCAR does release its own estimates.
But secrecy breeds curiosity, and perhaps even nosiness, so the Pocono Record conducted its own count based on aerial photographs and crowd-counting techniques.
The images, captured near the start of the race, revealed half-filled grandstands and an infield with vast stretches of grass where vehicles once clustered during past races.
The newspaper estimates that only about 48,000 spectators — a figure that includes a nearly 15 percent cushion to account for a margin of error — were on hand for the Sunoco Red Cross Pennsylvania 500 that day. By Dan Berret, Pocono Record Writer