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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 Hill s and Mountain s, also known as peaks. It is a measure of the independent stature of a Summit . DEFINITION OF PROMINENCE There are several equivalent definitions:
PROMINENCE IN MOUNTAINEERING Prominence is interesting to some Mountaineers because it is an objective measurement that is strongly correlated with the subjective significance of a summit. Peaks with low prominences are either subsidiary tops of some higher summit or relatively insignificant independent summits. Peaks with high prominences tend to be the highest points around and are likely to have extraordinary views. For example, the world's second highest mountain is K2 (height 8,611 m, prominence 4,017 m) rather than Mount Everest 's South Summit (height 8,749 m, prominence about 10 m), a subsummit of the main summit, since only summits with a sufficient degree of prominence are regarded as independent mountains. Many Lists Of Mountains take topographic prominence as a criterion for inclusion, or ''cutoff''. John and Anne Nuttall's ''The Mountains of England and Wales'' uses a cutoff of 15 m (about 50 ft), and Alan Dawson's list of Marilyn s uses 150 m (about 500 ft). (Dawson's list and the term "Marilyn" are limited to the British Isles.) In the contiguous United States, the famous list of " Fourteener s" (14,000 foot / 4268 m peaks) uses a cutoff of 300 ft / 91 m (with some exceptions). Also in the U.S., 2000 feet (610 m) of prominence has become an informal threshold that signifies that a peak has major stature. Lists with a high topographic prominence cutoff tend to favour isolated peaks or those that are the highest point of their Massif ; a low value, such as the Nuttalls', results in a list with many summits that may be viewed by some as insignificant. While the use of prominence as a cutoff to form a list of peaks ranked by elevation is standard, and is the most common use of the concept, it is also possible to use prominence as a mountain measure in itself. This generates Lists Of Peaks Ranked By Prominence , which are qualitatively different from lists ranked by elevation. Such lists tend to emphasize isolated high peaks, such as range or island high points and Stratovolcano es. One advantage of a prominence-ranked list is that it needs no cutoff, since a peak with high prominence is automatically an independent peak. PARENT PEAK It is common to define a peak's parent as a particular peak in the higher terrain connected to the peak by the key col. If there are several higher peaks there are various ways of defining which one is the parent. These concepts give ways of putting all peaks on a landmass into a hierarchy, showing which peaks are '''subpeaks''' of which others. For example, in Figure 1, the middle peak is a subpeak of the right peak, which is in turn a subpeak of the left peak, which is the highest point on its landmass. In that example, there is no controversy over the hierarchy; in practice, there are different definitions of parent. These different definitions follow. Encirclement or island parentage Also called ''prominence island parentage'', this is the most mathematically natural definition, and is defined as follows. The key col of peak A is at the meeting place of two closed contours, one encircling A and the other containing at least one higher peak. The encirclement parent of A is the highest peak that is inside this other contour. In terms of the rising-sea model, the two contours together bound an island, with two pieces connected by an isthmus at the key col. The encirclement parent is the highest point on this entire island. For example, the encirclement parent of Mont Blanc , the highest peak in the Alps , is Mount Everest . Mont Blanc's key col is a piece of low ground near Lake Onega in northwestern Russia (at 113 m elevation), on the Divide between lands draining into the Baltic and Caspian Sea s. This is the meeting place of two 113 m contours, one of them encircling Mont Blanc; the other contour encircles Mount Everest. This example demonstrates that the encirclement parent can be very far away from the peak in question when the key col is low. This means that, while simple to define, the encirclement parent often does not satisfy the intuitive requirement that the parent peak should be close to the child peak. For example, one common use of the concept of parent is to make clear the location of a peak. If we say that Peak A has Mont Blanc for a parent, we would expect to find Peak A somewhere close to Mont Blanc. This is not always the case for the various concepts of parent, and is least likely to be the case for encirclement parentage. A special case occurs for the highest point on an oceanic island or continent. Some sources define no parent in this case; others treat Mount Everest as the parent of every such peak (with the ocean as the "key col"). The encirclement parent is the highest possible parent for a peak; all other definitions pick out a (possibly different) peak on the combined island, a "closer" peak than the encirclement parent (if there is one), which is still "better" than the peak in question. The differences lie in what criteria are used to define "closer" and "better." Prominence parentage and the territory concept Prominence parentage is defined in the following way. The parent peak of peak A is found by continuing along a ridgeline from the key col; the nearest peak to A found in such a manner that has a higher topographic prominence than A is the prominence parent. The concept of prominence parentage (which is the most commonly used definition in the British Isles ) can be made precise and understandable by picking a definite prominence ''cutoff'' (in Britain this is normally 150m, to tie in with the list of Marilyns which have 150m or more relative height) and working out all the peaks that have greater prominence than that cutoff. The island or landmass in question can then be divided into ''territories'' by tracing the runoff of water from both sides of the ''key cols'' (see above) of each of the aforementioned peaks (usually there is a river running down from the col to facilitate this). This gives each peak its own territory; these can be of vastly varying sizes depending on the distribution of such peaks within the landmass). Put simply, ''for any peak whose prominence is less than the above cutoff, its prominence parent is the peak whose territory it resides in.'' This gives an unambiguous defintion of the parent peak. In Britain, for example, every peak that is not a Marilyn has a 'parent Marilyn' whose territory it resides in. ''This concept can be expanded to give the prominence parent of any peak'' (that is not the highest point of its island). Simply pick a cutoff that is one metre higher than the prominence of the peak you're trying to find the parent of, work out the territories, and the parent is the peak whose territory your peak resides in. This was used to work out the parentages on the List Of Peaks By Prominence . This is the long explanation; normally it will suffice to find the nearest higher and more prominent neighbour. However, some regions are topographically awkward. Height parentage Height parentage is a less widely used term. It is similar to prominence parentage, but it requires some sort of prominence cutoff criterion. The height parent is the closest peak to peak A (along all ridges connected to A) that has a greater height than A, and is above the prominence cutoff. For example, Mont Blanc 's height-parent is either a minor peak in the north-west Caucasus (if the prominence cutoff is low), or Mount Elbrus (if the cutoff is high). The disadvantage of this concept is that it goes against the intuition that a parent peak should always be more significant than its child. However it can be used to build an entire lineage for a peak which contains a great deal of information about the peak's position. Other criteria To choose among possible parents, instead of choosing the closest possible parent, it is possible to chose the one which requires the least descent along the ridge. In general, the analysis of parents and lineages is intimately linked to studying the Topology of Watersheds . Further discussion of parents can be found in the Orometry article at peaklist.org . INTERESTING PROMINENCE SITUATIONS The key col and parent peak are often close to the subpeak but this is not always the case, especially when the key col is relatively low. It is only with the advent of computer programs and geographical databases that thorough analysis has become possible.
While it is natural for Aconcagua to be the parent of Mount McKinley, since Mount McKinley is a major peak, consider the following situation: Peak A is a small hill on the coast of Alaska, with elevation 100 m and key col 50 m. Then the encirclement parent of Peak A is also Aconcagua, even though there will be many peaks closer to Peak A which are much higher and more prominent than Peak A (for example, Mount McKinley). This illustrates the disadvantage in using the encirclement parent.
CALCULATIONS AND MATHEMATICS OF PROMINENCE When the key col for a peak is close to the peak itself, prominence is easily computed by hand using a Topographic Map . However, when the key col is far away, or when one wants to calculate the prominence of many peaks at once, a computer is quite useful. Edward Earl has written a program called WinProm which can be used to make such calculations, based on a Digital Elevation Model . The underlying mathematical theory is called " Surface Network Modeling ," and is closely related to Morse Theory . A note about methodology: when using a Topographic Map to determine prominence, one often has to estimate the height of the key saddle (and sometimes, the height of the peak as well) based on the contour lines. Assume for simplicity that only the saddle elevation is uncertain. There are three simple choices: the ''pessimistic'', or ''clean'' prominence, assumes that the saddle is as high as it can be, i.e. its elevation is that of the higher contour line nearest the saddle. This gives a lower bound on the possible prominence of the peak.This assumes that the map itself is accurate; inaccuracies in mapping lead to further uncertainties and a larger error bound. ''Optimistic'' prominence assumes that the saddle is as low as possible, yielding an upper bound value for the prominence. ''Midrange'' or ''mean'' prominence uses the mean of these two values. Which methodology is used depends on the person doing the calculation and on the use to which the prominence is put. For example, if one is making a list of all peaks with at least 2,000 ft (610 m) of prominence, one would usually use the optimistic prominence, to include all possible candidates (knowing that some of these could be dropped off the list by further, more accurate, measurements). DEBATES ABOUT THE USE OF PROMINENCE The use of topographic prominence as a cutoff to eliminate subpeaks is well-established. This and the following sections address the merits and criticisms of using prominence as a primary mountain metric, for example, in creating lists of mountains ranked by prominence. Merits
Criticism The use of topographic prominence as a primary mountain metric has been widely criticised, for the following reasons.
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