User talk:Droll/sandbox

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I've been doing some research on mountain elevations and have discovered that:

  1. There are two standards in use for elevation data.
  1. NGVD 29 - National Geodetic Vertical Datum of 1929 AKA Sea Level Datum of 1929
  2. NAVD 88 - North American Vertical Datum of 1988 the datum currently in use by the NGS and appears on their datasheets.

All the USGS TOPO maps I have checked use NGVD 29. I recieved this information from the webmaster at Peakbagger.com"

“ Hi, Dave,

The elevations for virtually all peaks listed on Peakbagger.com that are in the United States come from the 1:24,000 USGS topographic maps (1:62,500 maps in most of Alaska). If there is a benchmark or spot elevation at the summit, that exact elevation is used, otherwise, I use the highest contour line at the summit as the elevation and record the contour interval, so, for example, a summit may be listed as "10,520+ feet" and "Elevation in range between 10,520 and 10,560 feet. (40-foot closed contour)".

In a few rare cases, field observations may have shown that the USGS map is in error, or elevations may need to be adjusted to account for observed differences in elevations of nearby peaks. But there are likely only about a handful of these cases. The vast majority are straight from the topo map.

There are instances of peaks with exact metric elevations on the 1:100,000 scale maps that do not have elevations on the 1:24,000 maps, or instances where a benchmark has an elevation in the USGS database but is not labeled on the map. In both these cases, I do not list the exact elevation, instead using the contour interval from the 1:24,000 map. I could reduce the number of contour interval peaks if I used exact elevations from these sources, but I have not done much work there.

Also, since all the 1:24,000 maps use the old NGVD29 vertical datum and not the newer NAVD88, my elevations are also based on the old datum. See the footnote 1 on this web page: http://www.peaklist.org/USlists/USP5000.html

Overseas, I follow the same rules, relying on the largest scale topo maps I can find for a country. But most of my overseas peaks have not been systematically checked. If the latitude-longitude for a peak is reported in precise decimal degrees on my site, then the elevation of that peak has usually also been verified to a high level of precision using large scale topo maps and I am very confident of its accuracy.

I hope this helps. Let me know if you have any other questions.

--Greg

 ”

As has already been discussed NGS data sheets appear to be the best source of elevations. I'll write section here within a few days about how to easily find data sheets. They do not exist for all summits.

I propose that NAVD 88 be the datum perfered in WikiProject Mountain articles. A similar policy already exists for the use of the WGS84 datum for latitude and longitude. This is a WikiProject Geographical coordinates policty. I have read that the differece in elevation can range from -5 feet to +15 feet. In my own limited experience the difference in elevations is usually in the order of 5 feet or so in the U.S. and Canada. I have not spent much time researching what kind of data is available on other continents. In many places I am sure this distinction is of little importance.

Obtaining NAVD 88 data is not that difficult. The USGS maintains a web service, Vertcon, which can be used to convert from one elevation datum to the other. It is important to remember to enter "feet" for "ft" after the elevation or the service will assume you have entered metres.