"For decades, the National Park Service provided official crowd estimates for gatherings on the National Mall but no longer does.

The policy changed after the Million Man March in 1995, a gathering of black men meant to show renewed commitment to family and solidarity. The park service estimated 400,000 people attended the march, making it one of the largest demonstrations in history in Washington.

But organizers believed they reached their goal of 1 million participants and threatened legal action. No lawsuit was filed, but the dispute was enough to get the park service out of the head-counting business."

Ref: http://www.denverpost.com/2017/01/21/national-park-service-t...