T&T: Height Above Sea Level

[Candy Chapman and Gary Bell]

Rob's posting:

A convenient tool for assessing heights above sea level is

http://www.earthtools.org/

I've been using it for waterfront lot locations, but it could also be valuable
for seeking out hurricane holes.

It will take a few minutes to figure out how to use, but is easy after a few
tries. Rob Brueckner

Gary's reply:

Gee, perhaps I haven't invested enough minutes figuring out how to use 
this webtool but when I tried the height tool near my home/marina, I got 
particularly goofy results.  Much of the land around my marina indicated 
a height of 5 to 6 meters, which is probably pretty good.  Sadly the 
adjacent water in Multnomah channel indicated anything up to 20 
meters.   Similarly for the main body of the Columbia River -- virtually 
adjacent height values from -2 to +20 meters, with most of the adjacent 
lands indicated as 5 meters.  The nearby airport is of course built on 
very flat land, but Earthtools indicates a wide variety of heights, 
varying by as much as 6 meters on the runway and adjacent ramps.  The 
system shows amazing diversity of values over a tiny lateral distance, 
giving the impression of great resolution.  The problem is that it 
hardly correlates with reality.  I did check for offsets and no, the 
dikes are not that high, and the anomalies don't seem to correlate to 
any nearby topography.   Rob, or other interested listees, would you 
truth test this around your home or other familiar place and report your 
results?  Are we beta testing this?