Topographical: British

In topography, prominence, also known as autonomous height, relative height or shoulder drop (in America) or prime factor (in Europe), is a concept used in the categorization of hills and mountains, also known as peaks. more...

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It is a measure of the independent stature of a summit. By definition, it is the elevation difference between the summit and the lowest contour that encircles it and no higher summit. It is also the smallest descent which one would have to make from a summit in order to re-ascend to a higher peak.

For example, it is standard that the world's second highest mountain is K2 (height 8,611 m, prominence 4,017 m) and not Mount Everest's South Summit (height 8,749 m, prominence about 10 m), a subsummit of the Main Summit. This is because only summits with a sufficient degree of prominence are regarded as independent mountains rather than subsidiary peaks.

Definition of prominence

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.;

For all peaks except Mount Everest, if the peak's prominence is P metres, to get from the summit to any higher terrain, one must descend at least P metres, whatever route is taken. Note that this implies that the prominence of any island or continental highpoint is equal to its elevation above sea level. In this definition, Mount Everest is a special case: its prominence is considered to be equal to its elevation, in order to agree with the previous definition.;

For all peaks except Mount Everest, the prominence can be calculated as follows. For every ridge (or path of any kind) connecting the peak to higher terrain, find the lowest point on the ridge. This will occur at a col (also called a saddle point or pass). The key col (or key saddle, or linking col, or link) is defined to be the highest among all of these cols, among 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 height.) The prominence is the difference between the elevation of the peak and the elevation of the key col. See Figure 1 below.;

Suppose that the sea level rises to the lowest level at which the peak becomes the highest point on an island. The prominence of that peak is the height of that island. The key col represents the last isthmus connecting the island to a higher island, just before they become disconnected.;

Prominence in mountaineering

Prominence is interesting to mountaineers because it is an objective measurement that is strongly correlated with the subjective significance of a summit. Peaks with low prominences are really just subsidiary tops of some higher summit. Peaks with high prominences tend to be the highest points around and are likely to have extraordinary views. In the U.S., 2000 feet (610 m) of prominence has become an informal threshold that signifies that a peak has major stature.

Read more at Wikipedia.org