I saw the beginning of the March on the west side, at 7th and Greenwich.  I then walked around the south side of the March, where many streets were blocked off, and got back near the March on the east side of  Fifth Avenue, walking northward from Washington Square to the end of the March past 28th St.

A couple of hours later, I went to the west side of Fifth Avenue, starting at 28th St. and walking south.  At this point, the March had been going on for 6 hours, and the crowds had thinned a little but were still large.