By convention, the prominence of Mount Everest, the Earth's highest mountain, is taken to equal the elevation of its summit above sea level. Apart from this special case, there are several equivalent definitions:
The prominence of a peak is the height of the peak’s summit above the lowest contour line encircling it and no higher summit.
If the peak's prominence is P metres, to get from the summit to any higher terrain one must descend at least P metres. Together with the convention for Mount Everest, this implies that the prominence of any island or continental highpoint is equal to its elevation above sea level.
For every ridge (or path of any kind) connecting the peak to higher terrain, find the lowest point on the ridge. This will be at a col (also called a saddle point or pass). The key col (or key saddle, or linking col, or link) is defined as the highest of these cols, along all connecting ridges. (If the peak is the highest point on a landmass, the key col will be the ocean, and the prominence of the peak is equal to its elevation.) The prominence is the difference between the elevation of the peak and the elevation of the......