Wow! I had no idea there was so much difference between the USGS DEM elevation data and SRTM elevation data.
Further, from the looks of it, SRTM data can be very off (given that USGS DEM data seems to better pass the "smell test" for the example hereafter).
This issue was thrust to the fore when I was doing my triplog for "Pat's Run 2012," the "all-in" version. Although the SRTM data looked weird for the run's route proper (the 4.2 mile course), it really seemed off for the all-in version.
To see what I mean, go to http://hikearizona.com/map.php?GPS=11909
and look at the profile in Route Manager. Then "ReSync SRTM" and look at the profile again. Quite different.
What tipped me off to this problem is that I don't think there's any way I did 921 feet of AEG that morning during the run or just wandering around before and after the run.
So I took the time to sync the track to USGS DEM data and got results that make much more sense.
Does the magnitude of this problem vary from area to area (with Tempe Town Lake being a particularly bad area) or is it like this pretty much all over?
Also, which dataset is really better for our purposes? Is it possible that I, in fact, did do an AEG of 921 feet that Saturday morning?
Decisionmaking and action should only be informed by, not subject to, healthy, reasonable concern.
That being said, anything worth doing is worth doing to excess.