[Talk-us] Incorrect Summit Elevations - Colorado

SteveC steve at asklater.com
Wed Feb 10 14:45:58 GMT 2010


On Feb 9, 2010, at 8:35 PM, Mike Thompson wrote:

> It appears that there is a systematic error in the summit elevations
> in OSM, at least in Colorado.

Well I was given a map, a guide book and a diary for xmas all for climbing every 14er, so... I can go fix those :-)

Talking about CO it's this weeks project of the week to help map Denver buildings:

	http://wiki.openstreetmap.org/wiki/Project_of_the_week


>  For example, Longs Peak is listed in
> OSM as having an elevation of 4340 meters (14,239 ft).  The topo map
> has it as 14,251 ft.  I have noticed the same type of issue with
> nearby peaks.  I suspect this has to do with the GNIS import.  The
> elevations in the GNIS are from the National Elevation Dataset (NED),
> not spot (e.g. summit) elevations.  The NED gives the (presumably
> average) elevation for a 3x3 arc second area.  According to the
> metadata for the GNIS:
> 
> ======================
> Elevation figures are not official and do not represent precisely
> measured or surveyed values. The data are extracted from the National
> Elevation Dataset (<http://ned.usgs.gov/>) for the primary coordinates
> and may differ from elevations cited in other sources. The differences
> will be most evident for features such as summits where precision is
> of more concern and where the local relief (rate of change of
> elevation) may be more prominent. However, the elevation figures are
> within tolerances for the data for most points and sufficiently
> accurate for purposes of general information.
> ======================
> 
> Precise and official elevations are very important for hikers and
> mountineers, or at least we like to think they are.
> 
> I believe that the National Geodetic Survey holds data on the official
> elevations for summits within the U.S., but I need to look into that.
> I am happy to start working on fixing this issue, but I didn't want to
> commence if someone else is already working on.
> 
> Mike
> 
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