There are a couple of inaccuracies with the photos provided as compared to the circles overlayed on the map.
First, the photo of the Beck rally as displayed ends with the WWII monument, but the ellipses on the map ends at the Washington monument, which proportionately increases the comparison quite a bit. The throng may well have extended that far, but the photo stops there.
Second, the Stewart rally at its crux was much larger than the photo being shown in contrast. I was there during that crux, and personally witnessed a completely congested mall - shoulder to shoulder - from the smithsonian stop (around 12th street) all the way to the congress building. That’s roughly double the size outlined in the photo.
I haven’t really put much thought to comparisons between the two events, as I consider them to be apples and oranges, but this sort of exaggerating is not helpful in establishing a position to change people’s minds about their beliefs on the matter at hand. It just fuels the bunk rhetoric.