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81-767: Some Furth definitions add a topographical prominence above 30 metres (98 feet), akin to a Scottish Murdo , however the official Scottish Mountaineering Club ("SMC") lists includes Furths with a prominence below this level. Applying the Real Munro definition to a Furth, requires a prominence above 150 metres (492 feet), akin to a Marilyn , and these 14 Furths are marked with (‡) in the tables below. The SMC lists 34 Furths: six in England, 15 in Wales, and 13 on Ireland. These compare with 282 Munros and 226 Munro Tops in Scotland. Thirty three have

162-436: A choropleth map . In meteorology, the word isopleth is used for any type of contour line. Meteorological contour lines are based on interpolation of the point data received from weather stations and weather satellites . Weather stations are seldom exactly positioned at a contour line (when they are, this indicates a measurement precisely equal to the value of the contour). Instead, lines are drawn to best approximate

243-452: A topographic map . However, when the key col is far away, or when one wants to calculate the prominence of many peaks at once, software can apply surface network modeling to a digital elevation model to find exact or approximate key cols. Since topographic maps typically show elevation using contour lines , the exact elevation is typically bounded by an upper and lower contour, and not specified exactly. Prominence calculations may use

324-691: A word without a repeated letter . As late as 1944, John K. Wright still preferred isogram , but it never attained wide usage. During the early 20th century, isopleth ( πλῆθος , plethos , 'amount') was being used by 1911 in the United States, while isarithm ( ἀριθμός , arithmos , 'number') had become common in Europe. Additional alternatives, including the Greek-English hybrid isoline and isometric line ( μέτρον , metron , 'measure'), also emerged. Despite attempts to select

405-420: 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." The (prominence) parent peak of peak A can be found by dividing the island or region in question into territories, by tracing the two hydrographic runoffs, one in each direction, downwards from the key col of every peak that

486-401: A "contour") joins points of equal elevation (height) above a given level, such as mean sea level . A contour map is a map illustrated with contour lines, for example a topographic map , which thus shows valleys and hills, and the steepness or gentleness of slopes. The contour interval of a contour map is the difference in elevation between successive contour lines. The gradient of

567-489: A "hierarchy" of peaks going back to the highest point on the island. One such chain in Britain would read: Billinge Hill → Winter Hill → Hail Storm Hill → Boulsworth Hill → Kinder Scout → Cross Fell → Helvellyn → Scafell Pike → Snowdon → Ben Nevis . At each stage in the chain, both height and prominence increase. Line parentage, also called height parentage, is similar to prominence parentage, but it requires

648-605: A Real Monro (these are Marilyns, and/or P600s) There are 13 Furths in Ireland listed by the Scottish Mountaineering Club , which are also referred to as the Irish Munros. Maolán Bui (centre: 4th from left) (‡) Have the prominence of over 150 metres (492 ft) to qualify as a Real Munro (these are Marilyns, and/or P600s) The DoBIH uses the following codes for the various classifications of mountains and hills in

729-463: A breakdown of Furths by country, and also marking the highest mountain classification grade by prominence (e.g. P600, Mayilyn, Hewitt etc.). (‡) Have the prominence of over 150 metres (492 ft) to qualify as a Real Munro (these are Marilyns, and/or P600s) The 15 Welsh Furths (or Welsh Munros) are part of the Welsh 3000 Challenge . (‡) Have the prominence of over 150 metres (492 ft) to qualify as

810-654: A chart of magnetic variation. The Dutch engineer Nicholas Cruquius drew the bed of the river Merwede with lines of equal depth (isobaths) at intervals of 1 fathom in 1727, and Philippe Buache used them at 10-fathom intervals on a chart of the English Channel that was prepared in 1737 and published in 1752. Such lines were used to describe a land surface (contour lines) in a map of the Duchy of Modena and Reggio by Domenico Vandelli in 1746, and they were studied theoretically by Ducarla in 1771, and Charles Hutton used them in

891-411: A constant pressure surface chart. Isohypse and isoheight are simply known as lines showing equal pressure on a map. An isotherm (from Ancient Greek θέρμη (thermē)  'heat') is a line that connects points on a map that have the same temperature . Therefore, all points through which an isotherm passes have the same or equal temperatures at the time indicated. An isotherm at 0 °C

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972-407: A curve of constant electric potential . Whether crossing an equipotential line represents ascending or descending the potential is inferred from the labels on the charges. In three dimensions, equipotential surfaces may be depicted with a two dimensional cross-section, showing equipotential lines at the intersection of the surfaces and the cross-section. The general mathematical term level set

1053-514: A distance of 360 m (1200 feet). The key col may also be close to the subject peak or far from it. The key col for Aconcagua, if sea level is disregarded, is the Bering Strait at a distance of 13,655 km (8,485 miles). The key col for the South Summit of Mount Everest is about 100 m (330 feet) distant. A way to visualize prominence is to imagine raising sea level so

1134-431: A given location and is used in the generation of isochrone maps . An isotim shows equivalent transport costs from the source of a raw material, and an isodapane shows equivalent cost of travel time. Contour lines are also used to display non-geographic information in economics. Indifference curves (as shown at left) are used to show bundles of goods to which a person would assign equal utility. An isoquant (in

1215-408: A great deal of information about the peak's position. In general, the analysis of parents and lineages is intimately linked to studying the topology of watersheds . Alteration of the landscape by humans and presence of water features can give rise to issues in the choice of location and height of a summit or col. In Britain, extensive discussion has resulted in a protocol that has been adopted by

1296-479: A hierarchy which defines some peaks as subpeaks of others. For example, in Figure ;1, the middle peak is a subpeak of the right peak, which is a subpeak of the left peak, which is the highest point on its landmass. In that example, there is no controversy about the hierarchy; in practice, there are different definitions of parent. These different definitions follow. Also known as prominence island parentage , this

1377-418: A highest submerged col of about 40 m, or only 8888 m below the peak of Everest. As a result, Mauna Kea's prominence might be subjectively more impressive than Everest's, and some authorities have called it the tallest mountain from peak to underwater base. Dry prominence is also useful for measuring submerged seamounts . Seamounts have a dry topographic prominence, a topographic isolation , and

1458-828: A line of constant annual variation of magnetic declination . An isoclinic line connects points of equal magnetic dip , and an aclinic line is the isoclinic line of magnetic dip zero. An isodynamic line (from δύναμις or dynamis meaning 'power') connects points with the same intensity of magnetic force. Besides ocean depth, oceanographers use contour to describe diffuse variable phenomena much as meteorologists do with atmospheric phenomena. In particular, isobathytherms are lines showing depths of water with equal temperature, isohalines show lines of equal ocean salinity, and isopycnals are surfaces of equal water density. Various geological data are rendered as contour maps in structural geology , sedimentology , stratigraphy and economic geology . Contour maps are used to show

1539-399: A negative topographic elevation . Prominence values are accurate to perhaps 100m owing to uncertainties in ocean sounding depths. Contour line A contour line (also isoline , isopleth , isoquant or isarithm ) of a function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value. It is a plane section of

1620-426: A picture of the major thermodynamic factors in a weather system. An isobar (from Ancient Greek βάρος (baros)  'weight') is a line of equal or constant pressure on a graph, plot, or map; an isopleth or contour line of pressure. More accurately, isobars are lines drawn on a map joining places of equal average atmospheric pressure reduced to sea level for a specified period of time. In meteorology ,

1701-440: A point; this distinction has since been followed generally. An example of an isopleth is population density , which can be calculated by dividing the population of a census district by the surface area of that district. Each calculated value is presumed to be the value of the variable at the centre of the area, and isopleths can then be drawn by a process of interpolation . The idea of an isopleth map can be compared with that of

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1782-409: A 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 satisfies some prominence criteria. 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

1863-437: A prominence-ranked list is that it needs no cutoff since a peak with high prominence is automatically an independent 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 many higher peaks there are various ways of defining which one is the parent, not necessarily based on geological or geomorphological factors. The "parent" relationship defines

1944-489: A single standard, all of these alternatives have survived to the present. When maps with contour lines became common, the idea spread to other applications. Perhaps the latest to develop are air quality and noise pollution contour maps, which first appeared in the United States in approximately 1970, largely as a result of national legislation requiring spatial delineation of these parameters. Contour lines are often given specific names beginning with " iso- " according to

2025-421: A specific time interval, and katallobars , lines joining points of equal pressure decrease. In general, weather systems move along an axis joining high and low isallobaric centers. Isallobaric gradients are important components of the wind as they increase or decrease the geostrophic wind . An isopycnal is a line of constant density. An isoheight or isohypse is a line of constant geopotential height on

2106-461: A variety of scales, from large-scale engineering drawings and architectural plans, through topographic maps and bathymetric charts , up to continental-scale maps. "Contour line" is the most common usage in cartography , but isobath for underwater depths on bathymetric maps and isohypse for elevations are also used. In cartography, the contour interval is the elevation difference between adjacent contour lines. The contour interval should be

2187-479: Is Aconcagua (6,960 m), in Argentina , and its prominence is 6,138 m. (To further illustrate the rising-sea model of prominence, if sea level rose 56 m, North and South America would be separate continents and Denali would be 6138 m, its current prominence, above sea level. At a slightly lower level, the continents would still be connected and the high point of the combined landmass would be Aconcagua,

2268-446: Is a contour line for a variable which measures direction. In meteorology and in geomagnetics, the term isogon has specific meanings which are described below. An isocline ( κλίνειν , klinein , 'to lean or slope') is a line joining points with equal slope. In population dynamics and in geomagnetics, the terms isocline and isoclinic line have specific meanings which are described below. A curve of equidistant points

2349-452: Is a line joining points with constant wind speed. In meteorology, the term isogon refers to a line of constant wind direction. An isopectic line denotes equal dates of ice formation each winter, and an isotac denotes equal dates of thawing. Contours are one of several common methods used to denote elevation or altitude and depth on maps . From these contours, a sense of the general terrain can be determined. They are used at

2430-438: Is a line of equal or constant dew point . An isoneph is a line indicating equal cloud cover. An isochalaz is a line of constant frequency of hail storms, and an isobront is a line drawn through geographical points at which a given phase of thunderstorm activity occurred simultaneously. Snow cover is frequently shown as a contour-line map. An isotach (from Ancient Greek ταχύς (tachus)  'fast')

2511-518: Is a line of equal temperature beneath the Earth's surface. An isohyet or isohyetal line (from Ancient Greek ὑετός (huetos)  'rain') is a line on a map joining points of equal rainfall in a given period. A map with isohyets is called an isohyetal map . An isohume is a line of constant relative humidity , while an isodrosotherm (from Ancient Greek δρόσος (drosos)  'dew' and θέρμη (therme)  'heat')

List of Furth mountains in the British Isles - Misplaced Pages Continue

2592-425: Is a measure of the independence of a summit . The key col ("saddle") around the peak is a unique point on this contour line and the parent peak is some higher mountain, selected according to various criteria. The prominence of a peak is the least drop in height necessary in order to get from the summit to any higher terrain. This can be calculated for a given peak in the following manner: for every path connecting

2673-485: Is a set of points all at the same distance from a given point , line , or polyline . In this case the function whose value is being held constant along a contour line is a distance function . In 1944, John K. Wright proposed that the term isopleth be used for contour lines that depict a variable which cannot be measured at a point, but which instead must be calculated from data collected over an area, as opposed to isometric lines for variables that could be measured at

2754-452: Is a sub-summit of the main summit (which has a height and prominence of 8,848 m). Many lists of mountains use topographic prominence as a criterion for inclusion in the list, 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 Marilyns uses 150 m (about 500 ft). (Dawson's list and the term "Marilyn" are limited to Britain and Ireland). In

2835-443: Is becoming preferred. There are two varieties of topographic prominence: wet prominence and dry prominence. Wet prominence is the standard topographic prominence discussed in this article. Wet prominence assumes that the surface of the earth includes all permanent water, snow, and ice features. Thus, the wet prominence of the highest summit of an ocean island or landmass is always equal to the summit's elevation. Dry prominence, on

2916-602: Is called the freezing level . The term lignes isothermes (or lignes d'égale chaleur) was coined by the Prussian geographer and naturalist Alexander von Humboldt , who as part of his research into the geographical distribution of plants published the first map of isotherms in Paris, in 1817. According to Thomas Hankins, the Scottish engineer William Playfair 's graphical developments greatly influenced Alexander von Humbolt's invention of

2997-406: Is defined as follows. In Figure 2 the key col of peak A is at the meeting place of two closed contours, one encircling A (and no higher peaks) 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 falling-sea model, the two contours together bound an "island", with two pieces connected by an isthmus at

3078-404: Is equal to its wet prominence (4205 m) plus the depth of its highest submerged col (about 5125 m). Totaling 9330 m, this is greater than any mountain apart from Everest. The dry prominence of Aconcagua is equal to its wet prominence (6960 m) plus the depth of the highest submerged col of the Bering Strait (about 40 m), or about 7000 m. It is worth noting Mauna Kea

3159-553: Is equal to its wet prominence plus the depth of its highest submerged col. Because Earth has no higher summit than Mount Everest , Everest's prominence is either undefined or its height from the lowest contour line. In a dry Earth, the lowest contour line would be the deepest hydrologic feature, the Challenger Deep , at 10,924 m depth. Everest's dry prominence would be this depth plus Everest's wet prominence of 8848 m, totaling 19,772 m. The dry prominence of Mauna Kea

3240-508: Is especially important in riparian zones. An isoflor is an isopleth contour connecting areas of comparable biological diversity. Usually, the variable is the number of species of a given genus or family that occurs in a region. Isoflor maps are thus used to show distribution patterns and trends such as centres of diversity. In economics , contour lines can be used to describe features which vary quantitatively over space. An isochrone shows lines of equivalent drive time or travel time to

3321-454: Is indicated on maps with isoplats . Some of the most widespread applications of environmental science contour maps involve mapping of environmental noise (where lines of equal sound pressure level are denoted isobels ), air pollution , soil contamination , thermal pollution and groundwater contamination. By contour planting and contour ploughing , the rate of water runoff and thus soil erosion can be substantially reduced; this

List of Furth mountains in the British Isles - Misplaced Pages Continue

3402-406: Is more prominent than peak A. The parent is the peak whose territory peak A is in. For hills with low prominence in Britain, a definition of "parent Marilyn " is sometimes used to classify low hills ("Marilyn" being a British term for a hill with a prominence of at least 150 m). This is found by dividing the region of Britain in question into territories, one for each Marilyn . The parent Marilyn

3483-457: Is not used because there is no obvious choice of cutoff. This choice of method might at first seem arbitrary, but it provides every hill with a clear and unambiguous parent peak that is taller and more prominent than the hill itself, while also being connected to it (via ridge lines). The parent of a low hill will also usually be nearby; this becomes less likely as the hill's height and prominence increase. Using prominence parentage, one may produce

3564-466: Is often used to describe the full collection of points having a particular potential, especially in higher dimensional space. In the study of the Earth's magnetic field , the term isogon or isogonic line refers to a line of constant magnetic declination , the variation of magnetic north from geographic north. An agonic line is drawn through points of zero magnetic declination. An isoporic line refers to

3645-524: Is relatively close to its submerged key col in the Pacific Ocean, and the corresponding contour line that surrounds Mauna Kea is a relatively compact area of the ocean floor. Whereas a contour line around Everest that is lower than 9330m from Everest's peak would surround most of the major continents of the Earth. Even just surrounding Afro-Eurasia would run a contour line through the Bering Straight, with

3726-412: Is shown in all areas. Conversely, for an island which consists of a plateau surrounded by steep cliffs, it is possible to use smaller intervals as the height increases. An isopotential map is a measure of electrostatic potential in space, often depicted in two dimensions with the electrostatic charges inducing that electric potential . The term equipotential line or isopotential line refers to

3807-535: 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; see Figure 1. The parent peak may be either close or far from the subject peak. The summit of Mount Everest is the parent peak of Aconcagua in Argentina at a distance of 17,755 km (11,032 miles), as well as the parent of the South Summit of Mount Everest at

3888-677: Is the Marilyn whose territory the hill's summit is in. If the hill is on an island (in Britain) whose highest point is less than 150 m, it has no parent Marilyn. Prominence parentage is the only definition used in the British Isles because encirclement parentage breaks down when the key col approaches sea level. Using the encirclement definition, the parent of almost any small hill in a low-lying coastal area would be Ben Nevis , an unhelpful and confusing outcome. Meanwhile, "height" parentage (see below)

3969-964: The Schiehallion experiment . In 1791, a map of France by J. L. Dupain-Triel used contour lines at 20-metre intervals, hachures, spot-heights and a vertical section. In 1801, the chief of the French Corps of Engineers, Haxo , used contour lines at the larger scale of 1:500 on a plan of his projects for Rocca d'Anfo , now in northern Italy, under Napoleon . By around 1843, when the Ordnance Survey started to regularly record contour lines in Great Britain and Ireland , they were already in general use in European countries. Isobaths were not routinely used on nautical charts until those of Russia from 1834, and those of Britain from 1838. As different uses of

4050-514: The barometric pressures shown are reduced to sea level , not the surface pressures at the map locations. The distribution of isobars is closely related to the magnitude and direction of the wind field, and can be used to predict future weather patterns. Isobars are commonly used in television weather reporting. Isallobars are lines joining points of equal pressure change during a specific time interval. These can be divided into anallobars , lines joining points of equal pressure increase during

4131-411: The three-dimensional graph of the function f ( x , y ) {\displaystyle f(x,y)} parallel to the ( x , y ) {\displaystyle (x,y)} -plane. More generally, a contour line for a function of two variables is a curve connecting points where the function has the same particular value. In cartography , a contour line (often just called

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4212-492: The 30 metres (98 feet) in prominence to be Murdos. Fifteen have the 150 metres (492 feet) of prominence to be Real Munros: four in England, six in Wales, and five in Ireland. Ten have the 600 metres (1,969 feet) in prominence to be P600s , which being over 3,000 ft, makes them "Super-Majors": three in England, three in Wales, and four in Ireland. Climbers who complete all Munros, and the SMC list of 34 Furths, are called Furthists ;

4293-649: The British Isles , which many of the above peaks also fall into: suffixes: = twin Topographical prominence In topography , prominence or relative height (also referred to as autonomous height , and shoulder drop in US English, and drop in British English) measures the height of a mountain or hill's summit relative to the lowest contour line encircling it but containing no higher summit within it. It

4374-419: The SMC keeps a register which numbered 631 Furthists at October 2018. The first Furthist is registered as James A. Parker who completed all 34 Furths on 19 April 1929 (having become a Munroist in 1927). In 1986, Ashley Cooper became the first person to climb all the 3,000 ft summits in one continuous expedition, of 111 days, 2,500 km (1,600 mi), and 150 km (93 mi) of ascent. This list

4455-452: The below ground surface of geologic strata , fault surfaces (especially low angle thrust faults ) and unconformities . Isopach maps use isopachs (lines of equal thickness) to illustrate variations in thickness of geologic units. In discussing pollution, density maps can be very useful in indicating sources and areas of greatest contamination. Contour maps are especially useful for diffuse forms or scales of pollution. Acid precipitation

4536-408: 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. Figure 3 shows a schematic range of peaks with

4617-410: The color underlying the minor peaks indicating the encirclement parent. In this case the encirclement parent of M is H whereas an intuitive view might be that L was the parent. Indeed, if col "k" were slightly lower, L would be the true encirclement parent. The encirclement parent is the highest possible parent for a peak; all other definitions indicate a (possibly different) peak on the combined island,

4698-400: The contiguous United States, the famous list of " fourteeners " (14,000 foot / 4268 m peaks) uses a cutoff of 300 ft / 91 m (with some exceptions). Also in the U.S., 2000 ft (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 favor isolated peaks or those that are

4779-482: The disadvantage in using the encirclement parent. A hill in a low-lying area like the Netherlands will often be a direct child of Mount Everest , with its prominence about the same as its height and its key col placed at or near the foot of the hill, well below, for instance, the 113-meter-high key col of Mont Blanc . When the key col for a peak is close to the peak itself, prominence is easily computed by hand using

4860-475: The encirclement parent.) While it is natural for Aconcagua to be the parent of Denali, since Denali 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, Denali). This illustrates

4941-487: The function is always perpendicular to the contour lines. When the lines are close together the magnitude of the gradient is large: the variation is steep. A level set is a generalization of a contour line for functions of any number of variables. Contour lines are curved, straight or a mixture of both lines on a map describing the intersection of a real or hypothetical surface with one or more horizontal planes. The configuration of these contours allows map readers to infer

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5022-489: The high contour (giving in a pessimistic estimate ), the low contour (giving an optimistic estimate), their mean (giving a "midrange" or "rise" prominence ) or an interpolated value (customary in Britain). The choice of method depends largely on the preference of the author and historical precedent. Pessimistic prominence, (and sometimes optimistic prominence) were for many years used in USA and international lists, but mean prominence

5103-662: 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 stratovolcanoes . One advantage of

5184-424: The highest points around and are likely to have extraordinary views. Only summits with a sufficient degree of prominence are regarded as independent mountains. For example, the world's second-highest mountain is K2 (height 8,611 m, prominence 4,017 m). While Mount Everest 's South Summit (height 8,749 m, prominence 11 m ) is taller than K2, it is not considered an independent mountain because it

5265-452: The image at right) is a curve of equal production quantity for alternative combinations of input usages , and an isocost curve (also in the image at right) shows alternative usages having equal production costs. In political science an analogous method is used in understanding coalitions (for example the diagram in Laver and Shepsle's work ). In population dynamics , an isocline shows

5346-429: The isotherm. Humbolt later used his visualizations and analyses to contradict theories by Kant and other Enlightenment thinkers that non-Europeans were inferior due to their climate. An isocheim is a line of equal mean winter temperature, and an isothere is a line of equal mean summer temperature. An isohel ( ἥλιος , helios , 'Sun') is a line of equal or constant solar radiation . An isogeotherm

5427-495: 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 (371 ft) elevation), on the divide between lands draining into the Baltic and Caspian Seas . This is

5508-440: The latter case, the method of interpolation affects the reliability of individual isolines and their portrayal of slope , pits and peaks. The idea of lines that join points of equal value was rediscovered several times. The oldest known isobath (contour line of constant depth) is found on a map dated 1584 of the river Spaarne , near Haarlem , by Dutchman Pieter Bruinsz. In 1701, Edmond Halley used such lines (isogons) on

5589-442: The locations of exact values, based on the scattered information points available. Meteorological contour maps may present collected data such as actual air pressure at a given time, or generalized data such as average pressure over a period of time, or forecast data such as predicted air pressure at some point in the future. Thermodynamic diagrams use multiple overlapping contour sets (including isobars and isotherms) to present

5670-435: The main sources of prominence data in Britain and Ireland. Other sources of data commonly ignore human-made alterations, but this convention is not universally agreed upon; for example, some authors discount modern structures but allow ancient ones. Another disagreement concerns mountaintop removal , though for high-prominence peaks (and for low-prominence subpeaks with intact summits), the difference in prominence values for

5751-427: The map key. Usually contour intervals are consistent throughout a map, but there are exceptions. Sometimes intermediate contours are present in flatter areas; these can be dashed or dotted lines at half the noted contour interval. When contours are used with hypsometric tints on a small-scale map that includes mountains and flatter low-lying areas, it is common to have smaller intervals at lower elevations so that detail

5832-420: The meeting place of two 113 m (371 ft) 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

5913-482: The nature of the variable being mapped, although in many usages the phrase "contour line" is most commonly used. Specific names are most common in meteorology, where multiple maps with different variables may be viewed simultaneously. The prefix "' iso- " can be replaced with " isallo- " to specify a contour line connecting points where a variable changes at the same rate during a given time period. An isogon (from Ancient Greek γωνία (gonia)  'angle')

5994-402: The other hand, ignores water, snow, and ice features and assumes that the surface of the earth is defined by the solid bottom of those features. The dry prominence of a summit is equal to its wet prominence unless the summit is the highest point of a landmass or island, or its key col is covered by snow or ice. If its highest surface col is on water, snow, or ice, the dry prominence of that summit

6075-569: The parent peak and subject peak are two separate islands. Then lower it until a tiny land bridge forms between the two islands. This land bridge is the key col of the subject peak, and the peak's prominence is its elevation from that key col. Prominence is interesting to many mountaineers because it is an objective measurement that is strongly correlated with the subjective significance of a summit. Peaks with low prominence are either subsidiary tops of some higher summit or relatively insignificant independent summits. Peaks with high prominence tend to be

6156-428: The peak to higher terrain, find the lowest point on the path; the key col (or highest 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. On a given landmass, the highest peak's prominence will be identical to its elevation. An alternative equivalent definition

6237-413: The relative gradient of a parameter and estimate that parameter at specific places. Contour lines may be either traced on a visible three-dimensional model of the surface , as when a photogrammetrist viewing a stereo-model plots elevation contours, or interpolated from the estimated surface elevations , as when a computer program threads contours through a network of observation points of area centroids. In

6318-407: The same over a single map. When calculated as a ratio against the map scale, a sense of the hilliness of the terrain can be derived. There are several rules to note when interpreting terrain contour lines: Of course, to determine differences in elevation between two points, the contour interval, or distance in altitude between two adjacent contour lines, must be known, and this is normally stated in

6399-440: The technique were invented independently, cartographers began to recognize a common theme, and debated what to call these "lines of equal value" generally. The word isogram (from Ancient Greek ἴσος (isos)  'equal' and γράμμα (gramma)  'writing, drawing') was proposed by Francis Galton in 1889 for lines indicating equality of some physical condition or quantity, though isogram can also refer to

6480-497: The two conventions is typically relatively small. The key col and parent peak are often close to the sub-peak 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 . For example, the key col of Denali in Alaska (6,194 m) is a 56 m col near Lake Nicaragua . Denali's encirclement parent

6561-563: Was downloaded from the Database of British and Irish Hills ("DoBIH") in October 2018, and are peaks the DoBIH marks as being Furths ("F"). The SMC updates their list of official Furths from time to time, and the DoBIH also updates their measurements as more detailed surveys are recorded, so these tables should not be amended or updated unless the entire DoBIH data is re-downloaded again. The following are

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