The prominence of a peak may be defined as the minimum height necessary to descend to get from the summit to any higher terrain, which can be calculated for a given peak in the following way: for every path connecting the peak to higher terrain, find the lowest point on the path; the key col (or key saddle, or linking col, or link) is defined as the highest of these points, along all connecting paths; the prominence is the difference between the elevation of the peak and the elevation of its key col. See Figure 1. Under this definition, the prominence of Mount Everest is not defined as there is no higher point. An alternative definition, otherwise equivalent, is that the prominence is the height of the peak's summit above the lowest contour line encircling it, but containing no higher summit within it.