Topographic Prominence
In many ways prominence is a better measure of the "interestingness" of a mountain than its elevation. The highest mountains in the world are all in the Himalayas, and a list of the highest peaks shows little variety. In contrast, the most prominent peaks of the world (see Wikipedia ) are much more interesting.
The lowest point on a walk from a peak P to a higher peak is known as the key saddle (or sometimes key col). The prominence of P is the difference in elevation between P and the key saddle. It can be shown that each key saddle is unique; that is, it corresponds to only one peak.
The three most important objective measures of a mountain are its elevation, isolation, and prominence. Finding the height of mountains has a storied history going back to the development of trigonometry for surveying. Today we have very accurate methods based on satellites, and the elevation of every point on Earth is known to a reasonable degree of accuracy. Once the elevation of every point is known, finding isolation (the distance to a higher point) can be done by studying topographic maps, and this was done for selected large mountains as the Internet became popular. Prominence was also initially determined by looking at maps, trying to find the key saddle for each big mountain. This could be very difficult if the key saddle was far away. Starting in the 1990s, computers began to attack the problem, with the ultimate goal of finding the prominence of every mountain in the world.
From about 2005-2010 I worked on Google Earth, where one of my tasks was to build up a terrain database for Earth to use. We gathered terrain data from many different sources, merged them, and corrected many of their errors. In 2014, as I was getting more into peakbagging as a hobby, I noticed that the peakbagger.com Web site was missing prominence values for some of the minor mountains I had climbed in Europe. I wrote an email to Edward Earl, whom I had heard calculated many of the prominence values on the site. I soon learned that Edward had written a program called WinProm that could take terrain data and generate prominence values from all of the peaks within a given area. I offered to run Edward's algorithms over the Google Earth terrain database using thousands of computers in parallel to find the prominence of every little hill. Over the next few months Edward worked frantically to adapt his code to Google's environment. He was also working on some improvements he had in mind for awhile.
