As I have been using the topos from this site (all of them amazing, and very difficult to create), I have noticed some differences. In the Northwest and southwest topos, the contour lines are anywhere from two to 9 feet off of real elevation (to find this I make a waypoint on a contour line and then view it in google earth). When I do the same with the individual state topos, they have all been spot on, with the exception of one time when it was a foot off. I was wondering where each of them got there contour lines, and how they got off from each other. More of a curiosity question really.
I compared NW topo with Washington and Idaho. Idaho topo was spot on every time, and washington, I only had one spot that was one foot off. In NW, it was anywhere from two feet to nine feet. I compared Utah topo with SW topo and the Utah topo was accurate every time whereas SW topo was off about two to nine feet. I was just curious if they got their data from two different places, and if so where.