Brian Rachford's Prominence Score page

(Note: I think the ideas I'm laying out here are pretty much new, but if not, please let me know; 01/02/08)


Prominence is a derived quantity for a peak based on elevation measurements, namely how much elevation you would have to drop when traversing between the peak and the highest connecting saddle (the key saddle) to any higher peak. Or, you can think of it as the difference in height between the summit and the lowest closed elevation contour that completely encircles a peak. The word "prominence" seems to date from around 1980, but the idea has been around long before that as "drop", "saddle drop", "rise", "re-ascent", and other terms. In fact, major lists of peaks that use this as one criterion pre-date the use of the term "prominence". The idea is that prominence provides a measurement of the objective topographic significance of a peak regardless of elevation above sea level and it does a good job of that.

Why Prominence Score?

The group of people who are particularly enamored with prominence as the most important measure of a mountain also maintain lists of who has climbed the most peaks at or above a particular prominence level. If prominence truly defines a mountain, how can you really have climbed the mountain if you started above the key saddle? I've used the term "Prominence Ascent" (I am capitalizing my new terms for emphasis, but lower case is fine) on my personal hiking stats page for quite a while, as a suggested way of designating a mountain that one has actually climbed in the way implied by the definition of prominence; i.e., one either started at or below the level of the key saddle or descended to that level sometime during the hike.

How to calculate Prominence Score

The downside of the idea of a Prominence Ascent is that it is an either/or proposition. (Of course, prominence itself has a similar "winner-takes-all" issue in that a nearby peak that is only slightly lower than the main peak might get a low prominence value.) This is particularly acute when you consider a mountain with an extremely high prominence, like Aconcagua or Everest. I'm certainly not going to tell someone that they get no credit for the ascent just because they didn't start from sea level. However, implication of the definition of prominence is that they shouldn't get credit for a full ascent. That's where the Prominence Score comes in.

The calculation of Prominence Score is easy. If you were at or below the key saddle on the hike/climb, you get the full value of prominence for your Prominence Score. If not, you only get credit for the amount of the prominence that you actually climbed. E.g., for a 10,000-foot peak with a 7,000-foot key saddle, if you started at or below 7,000 feet, your score is 3,000 feet, but if you started at 8,500 feet, you only get 1,500 feet. You can do this for all of the peaks you have climbed to get your Total Prominence Score. You only get credit for your "best" ascent of a particular peak, no matter how many times you have climbed it. There is no restriction on whether you pass through the actual key saddle or not, just that you were at or below that elevation while hiking, no matter what route you take. Also, I intend this quantity to only apply to foot travel or climbing (i.e., horseback riding doesn't count, and while debatable, I would tend not to count cycling; motorized travel certainly doesn't count).

If you climb multiple peaks on one continuous hike, you will by definition have to drop to at least the level of the key saddle while traversing between peaks. So, you may or may not get a Prominence Ascent of the main peak, but the sub-peaks will all get their full prominence credit. A subtle point; when you climb multiple peaks, your lowest elevation should apply to the peak with the highest prominence. Thus, you don't get penalized for climbing the sub-peak first.

Another way to look at the concept is to calculate a Relative Prominence Score. This is simply the Prominence Score divided by the Prominence. I.e., what fraction of a true Prominence Ascent did you do? This will range from 0.0 for a total drive-up, to 1.0 for a true Prominence Ascent, with no extra credit given for any elevation below the key saddle.


One of the nice things about these types of Prominence Scores is that some of them give more credit to those who focus on climbing very prominent peaks, while others give higher scores to those who try to climb everything in a region, including low prominence peaks. There is something for everybody and the scores mostly give more credit (one way or the other) for people who do more elevation gain on their hikes/climb.

If you have a strong focus on peaks with large prominence, your Total Prominence Score should be high and your Mean Prominence Score will probably be high. However, your Total Relative Prominence Score and Mean Relative Prominence Score might be somewhat low just because it is more difficult to do a Prominence Ascent of a peak with high prominence. Also, your Mean Prominence Score might still be low if you are focusing on peaks that have roads that go high.

On the other hand, if you intently focus on climbing all peaks in an area, your Mean Prominence Score will be low, and your your Total Prominence Score will only be high if you are climbing a lot of low prominence peaks. On the other hand, your Mean Relative Prominence Score should be very high, and your Total Relative Prominence Score will probably be high as well.

Note that since the Prominence Scores are capped based on the actual prominence, you don't get extra credit if you do a long ascent on a minor peak, and it takes a lot of minor peaks to add up to the Prominence Score of a major peak. At the same time, you don't get much credit for driving up a prominent peak, either, and that also seems fair. Overall, I think these values give a little more mountaineering flavor to prominence as opposed to a purely topographic view that ignores the realities of climbing mountains.

Admittedly, it does take more effort to keep track of the various Prominence Scores, but considering the effort sometimes required to figure out Prominence in the first place, this seems like a reasonable add-on. The assumption here is that most people who are interested in prominence are already "numbers" sorts of people in the first place.

I'm not sure if I really expect anyone to really run with this concept. I'm certainly not prescribing this as a required way of assessing an ascent, and my own record of ascents isn't particularly impressive. But, if prominence is to really mean something for peakbaggers, the concept should be considered. Take this page as a bit of an agit to get people to think through the logical implications of defining mountains in certain ways.

Finally, I would like to give one instructive example. Pikes Peak has an interpolated prominence of 5530 feet (the key saddle elevation is not known precisely, but lies between 8560 and 8600 feet), the second highest in Colorado and the 37th highest in the lower 48 United States. One can drive all the way to the summit or take the cog railroad. That gets you a Prominence Score of 0 and a Relative Prominence Score of 0.0. Although the road patrol discourages it, you could start your hike from the summit road at 12930 feet. With the summit elevation of 14110 feet, your Prominence Score would be 1180 and your Relative Prominence Score would be 0.213 (the number of significant digits after the decimal point is a matter of personal preference, but probably should be at least two). The popular Crags route that starts further down the road and still piques the interest of the road patrol starts at 10100 feet, giving a Prominence Score of 4010 and a Relative Prominence Score of 0.725. Finally, the classic route is via the Barr Trail which starts at 6700 feet, thus an ascent gives you full credit; a Prominence Score of 5530 and a Relative Prominence Score of 1.0. Purists would argue that you also have to descend under your own power to get credit. Still, the point is that driving to the summit gives you no mountaineering credit, and if you believe prominence really defines the mountain, you have to start your hike at or below 8580 feet (the elevation of the key saddle) to claim full credit by your own definition.

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File last modified: 11 November 2008

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