[Tagging] Topographic Prominence for Peaks

Joseph Eisenberg joseph.eisenberg at gmail.com
Sun Sep 23 00:00:09 UTC 2018


I've been tagging peaks (natural=peak) with the key
prominence=<topographic prominence in meters>

Prominence is a natural feature with a use similar to elevation. When
I see ele=*, I know how high the top of the peak is, but not how tall
the peak is compared to the surrounding land. For example, a hill in
my valley may have ele=2000m, but it isn't a mountain: it's a 300m
hill that rises out of surrounding land at 1700m.

Prominence is calculated by subtracting the elevation of the lowest
saddle (or "col") from the elevation of the peak:

https://en.wikipedia.org/wiki/Topographic_prominence

"The prominence of a peak is the minimum height necessary to descend
to get from the summit to any higher terrain" or "the height of the
peak’s summit above the lowest contour line encircling it but
containing no higher summit within it."

Both of these definitions are the same for all peaks except for the
highest peak on a landmass, eg Mount Everest in Eurasia: in this case
use the second definition, which means that the tallest peak on a
(super-)continent or island is the same as it's elevation.

This started when I became interested in "peak bagging", where hikers
and climbers record the peaks they have summited. There are separate
categories based on the prominence of a peak. Gunungbagging.com in
Indonesia lists elevation, prominence and names for many peaks here in
Indonesia, and the site authors gave permission for the data to be
added to Openstreetmap.

There are other lists of prominent peaks for the rest of the world,
but please check if you can use the data based on the license, before
adding it to OSM.

Elevation and prominence can both be calculated from SRTM data, eg by
using Opentopomap tiles and finding the highest contour lines around a
peak, and the lowest near a saddle.

Prominence and elevation can be calculated by computer with good data,
but for my part of the world the SRTM data is not high enough quality
to get good results without cross-checking against aerial imagery.
Also the calculations are not simple, and are not precise for sharply
pointed peaks or deeply carved saddles, therefore I believe it will be
useful to include this data directly in tags.

I also find that calculation the prominence of peaks has encouraged me
to add more ridge lines and saddle points (with elevations), which
should make the database more useful in mountainous areas.

Do you think I should write up a formal proposal for this tag?

-Joseph



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