Originally Posted by
DiabloScott
My conclusion is that the altimeters used in most bike computers just aren't that good at producing consistent repeatable readings... that is I think their users assume they're more precise than they really are.
Now I've got dozens of Strava records up the local mountain from my Android-app, and they vary by 1% or so over 3800 feet of elevation change... it's hard to expect much more precision than that.
So altimeters and GPS-map data are more/less accurate/precise than each other in different situations.
Pretty much. And a lot depends too on the type of terrain. GPS map data is pretty accurate in areas like Kansas where you do not have a lot of mountain road cuts. The biggest inaccuracy's there is that the map data show highway overpasses as level. A good example of where the map data is way out of whack is here
http://ridewithgps.com/routes/3663331. This is my Strava track of the same.
http://www.strava.com/activities/12313945#z1458|1557. Notice it does dip going over the two canyons. not sure what caused this. The down grade is actually very constant on this section.