[Tagging] Topographic Prominence for Peaks

[Joseph Eisenberg]

For most peaks, it's only necessary to know the elevation of the
nearby saddles and peaks to find the prominence. For example, walk to
the top of the hill and record the elevation. Look around and find any
taller nearby peaks. If there is only 1 taller hill, walk down the
ridge line to the lowest point between the first hill and the taller
hill, then record the saddle elevation. Prominence is then elevation
of the first peak minus the elevation of the saddle.

It's more difficult for very prominent peaks, where the "key col" or
lowest saddle may be 1000's of kilometers away, but all of these peaks
already have prominence calculated and listed on Wikipedia:
https://en.wikipedia.org/wiki/List_of_peaks_by_prominence,
https://en.wikipedia.org/wiki/List_of_islands_by_highest_point,
https://en.wikipedia.org/wiki/List_of_Ultras_of_Africa

I just remembered that there was an abandoned proposal for this tag.
How do I revive the proposal? Just start editing the page,
https://wiki.openstreetmap.org/wiki/Proposed_features/key:prominence
Or make a new page?

Joseph

On 9/23/18, Warin <61sundowner at gmail.com> wrote:
> On 23/09/18 10:00, Joseph Eisenberg wrote:
>> 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?
>>
>
> Yes to documenting it.
>
> The evaluation of 'prominence' would be to some local area .. what is the
> size of that area?
>
> ----------------
> Some will say a formal proposal is 'best'. It is up to you to decide what is
> 'best'.
> But by all means discuss it here.
>
>
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