Editing Contour line (section)

=== Meteorology ===
[[File:Isohyet.png|thumb|upright=1.3|Isohyetal map of precipitation]]

Meteorological contour lines are based on [[interpolation]] of the point data received from [[weather station]]s and [[weather satellite]]s. 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 the locations of exact values, based on the scattered information points available.

[[Weather maps|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 a picture of the major thermodynamic factors in a weather system.

==== Barometric pressure ====<!-- [[Isobar (meteorology)]] redirects here -->
[[File:Loop isallobaric tendencies.gif|thumb|Video loop of isallobars showing the motion of a [[cold front]]]]
An '''isobar''' ({{ety|grc|''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]], the [[barometric pressure]]s shown are reduced to [[sea level]], not the surface pressures at the map locations.<ref>{{cite web |publisher=University of Wisconsin |author=Edward J. Hopkins, Ph.D. |date=1996-06-10 |url=http://www.meteor.wisc.edu/~hopkins/aos100/sfc-anl.htm |title=Surface Weather Analysis Chart |access-date=2007-05-10}}</ref>  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.<ref name="OMM">{{cite web | url= http://www.eumetcal.org/resources/ukmeteocal/rapid_cyclo/www/english/glossary/isalloba.htm | title= Isallobar | author= World Meteorological Organisation | author-link= World Meteorological Organisation | work= Eumetcal | access-date= 12 April 2014 | url-status= dead | archive-url= https://web.archive.org/web/20140416031654/http://www.eumetcal.org/resources/ukmeteocal/rapid_cyclo/www/english/glossary/isalloba.htm | archive-date= 16 April 2014 }}</ref> These can be divided into ''anallobars'', lines joining points of equal pressure increase during a specific time interval,<ref name="OMM-1">{{cite web | url= http://www.eumetcal.org/euromet/glossary/analloba.htm | archive-url= https://web.archive.org/web/20150924003018/http://www.eumetcal.org/euromet/glossary/analloba.htm | url-status= dead | archive-date= 24 September 2015 | title= Anallobar | author= World Meteorological Organisation | author-link= World Meteorological Organisation | work= Eumetcal | access-date= 12 April 2014 }}</ref> and ''katallobars'', lines joining points of equal pressure decrease.<ref name="OMM-2">{{cite web | url= http://www.eumetcal.org/euromet/glossary/katallob.htm | archive-url= https://web.archive.org/web/20080205124154/http://www.eumetcal.org/euromet/glossary/katallob.htm | url-status= dead | archive-date= 5 February 2008 | title= Katallobar | author= World Meteorological Organisation | author-link= World Meteorological Organisation | work= Eumetcal | access-date= 12 April 2014 }}</ref> In general, weather systems move along an axis joining high and low isallobaric centers.<ref>{{ cite web | url= http://apollo.lsc.vsc.edu/classes/met130/notes/chapter13/isallobars.html | title= Forecasting weather system movement with pressure tendency | work= Chapter 13 – Weather Forecasting | publisher = Lyndon State College Atmospheric Sciences | access-date = 12 April 2014}}</ref> 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 a constant pressure surface chart. Isohypse and isoheight are simply known as lines showing equal pressure on a map.

==== Temperature and related subjects ====
[[Image:arctic.svg|thumb|The {{convert|10|C}} mean isotherm in July, marked by the red line, is commonly used to define the border of the [[Arctic region]]]]

An '''isotherm''' ({{ety|grc|''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.<ref name="DataAir">{{cite web|author=DataStreme Atmosphere|publisher=American Meteorological Society|url=http://www.ametsoc.org/amsedu/dstreme/learn/sample.act.html |title=Air Temperature Patterns|date=2008-04-28|access-date=2010-02-07 |archive-url = https://web.archive.org/web/20080511124504/http://www.ametsoc.org/amsedu/dstreme/learn/sample.act.html |archive-date = 2008-05-11}}</ref><ref name="Hughes"/>  An isotherm at 0&nbsp;°C is called the [[freezing level]]. The term ''lignes isothermes'' (or ''lignes d'égale chaleur)'' was coined by the [[Prussia]]n 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.<ref>{{ cite book | last=Daum | first=Andreas W.|author-link=Andreas Daum | year=2024 | title=Alexander von Humboldt: A Concise Biography | location=Trans. Robert Savage. Princeton, N.J. | publisher=Princeton University Press |pages=106–107 | isbn=978-0-691-24736-6 }}</ref><ref>{{Cite journal|last=Munzar|first=Jan|date=1967-09-01|title=Alexander Von Humboldt and His Isotherms|journal=Weather|language=en|volume=22|issue=9|pages=360–363|doi=10.1002/j.1477-8696.1967.tb02989.x|issn=1477-8696|bibcode=1967Wthr...22..360M}}</ref> According to Thomas Hankins, the Scottish engineer [[William Playfair]]'s graphical developments greatly influenced Alexander von Humbolt's invention of the isotherm.<ref>{{Cite journal |date=1999 |title=Blood, Dirt, and Nomograms: A Particular History of Graphs |url=https://www.journals.uchicago.edu/doi/10.1086/384241 |journal=Isis |language=en |volume=90 |issue=1 |pages=50–80 |doi=10.1086/384241 |issn=0021-1753}}</ref> 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.<ref>{{Cite journal |last=Strobl |first=Michael |date=2021 |title=Alexander von Humbolt's Climatological Writings |url=https://onlinelibrary.wiley.com/doi/10.1111/glal.12313 |journal=German Life and Letters |language=en |volume=74 |issue=3 |pages=371–393 |doi=10.1111/glal.12313 |issn=0016-8777}}</ref> 

An '''isocheim''' is a line of equal mean winter temperature, and an '''isothere''' is a line of equal mean summer temperature.

An '''isohel''' ({{langx|grc|ἥλιος|helios|Sun|label=none}}) is a line of equal or constant [[solar radiation]].

An '''isogeotherm''' is a line of equal temperature beneath the Earth's surface.

==== Rainfall and air moisture ====
An '''isohyet''' or '''isohyetal line''' ({{ety|grc|''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''' ({{ety|grc|''δρόσος'' (drosos)|dew||''θέρμη'' (therme)|heat}}) 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.

==== Wind ====<!-- [[Isogon (meteorology)]] redirects here -->
An '''isotach''' ({{ety|grc|''ταχύς'' (tachus)|fast}}) is a line joining points with constant [[wind]] speed.
In meteorology, the term '''isogon''' refers to a line of constant wind direction.

==== Freeze and thaw ====
An '''isopectic''' line denotes equal dates of [[ice]] formation each winter, and an '''isotac''' denotes equal dates of thawing.