The first image below is making its away around the conservative blogosphere and e-mail lists. It claims to be a size comparison of Glenn Beck's rally to that of the "Rally to Restore Sanity" hosted by Jon Stewart.
Seems like Glenn Beck's "Restoring Honor" rally was bigger than Jon Stewart's. But let us examine the geography and image interpretation used for the image. For Beck's rally look how the oval starts to the left of the Lincoln Memorial, where the speaker's were and roads prevented people from being behind, and goes away past the World War II Memorial at the end of the reflecting pool, where the image ends. Now for Stewart's rally look how the at the right side of the photo, there is an oval building. The bulk of the rally ends at the street coming right after the circular building.. The building is the Hirshhorn Museum yet the oval in the image for Stewart's rally ends well before the museum.
Take a look at the mini-map below now with my modifications (a red block for Beck and yellow for Stewart). Size-wise Beck's rally is slightly bigger but Beck's rally had a reflecting pool in the middle of it.
This is not meant to be a political post. I do not even like getting involved in the beast known as population/crowd estimates. This post merely is to show how a map is being used to distort a current event.