“Up to” 200,000 people is a pretty wide target to hit, LOL
They should have said they expected up to a billion people.
That 200,000 figure was the number chosen by the organizers when they got their permit. From the article:
The permit for the gathering — which will make the moral case for reducing greenhouse gas emissions linked to global warming — is for 200,000 people. The Moral Action on Climate Network, along with the Earth Day Network, League of Conservation Voters, Sierra Club and other groups, have timed the rally on the Mall the same day of the pope’s speech.