[Tagging] Elevation and height on vertical features
gdt at ir.bbn.com
Fri Jan 8 17:54:36 UTC 2016
Mike Thompson <miketho16 at gmail.com> writes:
> On Fri, Jan 8, 2016 at 9:47 AM, Colin Smale <colin.smale at xs4all.nl> wrote:
>> How did all the elevation data get into OSM in the first place?
> The elevations of peaks in the US came from the GNIS import. In turn the
> GNIS elevations came from the National Elevation Dataset (NED) , and it
> mostly uses the North American Vertical Datum of 1988 . The other
> problem is that these are not "spot elevations" and therefore the elevation
> of a peak in the GNIS does not - in most cases - match the official
> elevation (the ones shown on the old USGS Topo maps and published by the
> National Geodetic Survey).
>  http://nationalmap.gov/elevation.html
>  http://www.usgs.gov/faq/categories/9865/4921
>  http://www.ngs.noaa.gov/datasheets/
Perhaps it would be a good project, perhaps via maproulette, to spiff
this up. It can be tricky, though, because the benchmarks on mountains
are not always the exact summit -- I actually found the mark on
Mt. Washburn in Yellowstone, and I don't think it matches the mountain
height. But I get it that the USGS surely publishes mountain heights
I do see that WGS84 heights and NAVD88 heights are off by part of a
meter east coast up to 2m in Washington State. Still, I think data with
those kinds of errors is far better than no data.
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