Map Pedometer - How far did you go?

Thanks. Elevation Graph is a very useful feature, and just knowing the accuracy in a polygon of county or whatever sourced the data would be helpful, because if the current water level is stated on some website, you might want to change your route. You already nailed the pedometer aspect on the site...

What is the source of elevation data, and what is the data accuracy? It seems to be off in some cases by 6 inches, which is fine for mountain hiking perhaps, but not for street flooding warning purposes.

I notice that when I crossed a bridge, the elevation feature thought I followed the ground and showed a 20 ft drop and rise.