Editing Contour line (section)

== History ==
[[File:Halley compass variations 1702.jpg|thumb|upright=1.1|[[Edmond Halley]]'s ''New and Correct Chart Shewing  the Variations of the Compass'' (1701)]]
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 [[Dutch (ethnic group)|Dutchman]] Pieter Bruinsz.<ref name=":0">{{Cite journal|url=http://www.age-geografia.es/ojs/index.php/bage/article/viewFile/2414/2262|title=Orígenes de la representación topográfica del terreno en algunos mapas hispanoamericanos del s. XVI|last=Morato-Moreno|first=Manuel|date=2017|journal=Boletín de la Asociación de Geógrafos Españoles|doi=10.21138/bage.2414|doi-access=free}}</ref> In 1701, [[Edmond Halley]] used such lines (isogons) on a chart of magnetic variation.<ref>Thrower, N. J. W. ''Maps and Civilization: Cartography in Culture and Society'', University of Chicago Press, 1972, revised 1996, page 97; and Jardine, Lisa ''Ingenious Pursuits: Building the Scientific Revolution'', Little, Brown, and Company, 1999, page 31.</ref>  The Dutch engineer [[Nicolaas Kruik|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 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, [[François Nicolas Benoît, Baron Haxo|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]].<ref name="Skel58">R. A. Skelton, "Cartography", ''History of Technology'', Oxford, vol. 6, pp. 612–614, 1958.</ref><ref>Colonel Berthaut, ''La Carte de France'', vol. 1, p. 139, quoted by Close.</ref><ref>C. Hutton, "An account of the calculations made from the survey and measures taken at Schehallien, in order to ascertain the mean density of the Earth", ''Philosophical Transactions of the Royal Society of London'', vol. 68, pp. [http://gallica.bnf.fr/ark:/12148/bpt6k55873m/f808.item 756]–[http://gallica.bnf.fr/ark:/12148/bpt6k55873m/f809.item 757]</ref>

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 chart]]s until those of [[Russia]] from 1834, and those of Britain from 1838.<ref name="Skel58"/><ref>C. Close, ''The Early Years of the Ordnance Survey'', 1926, republished by David and Charles, 1969, {{ISBN|0-7153-4477-3}}, pp. 141–144.</ref><ref>T. Owen and E. Pilbeam, ''Ordnance Survey: Map Makers to Britain since 1791'', HMSO, 1992, {{ISBN|0-11-701507-5}}.</ref>

As different uses of 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'' ({{ety|grc|''ἴσος'' (isos)|equal||''γράμμα'' (gramma)|writing, drawing}}) was proposed by [[Francis Galton]] in 1889 for lines indicating equality of some physical condition or quantity,<ref>{{cite journal|journal =Nature|volume= 40|date = 1889|page =651|first = Francis|last = Galton|title = On the Principle and Methods of Assigning Marks for Bodily Efficiency|issue= 1044|doi= 10.1038/040649a0|bibcode= 1889Natur..40..649.|s2cid= 3996216|url = https://babel.hathitrust.org/cgi/pt?id=uva.x001089260&view=1up&seq=891|doi-access = free}}</ref> though ''isogram'' can also refer to a [[isogram|word without a repeated letter]]. As late as 1944, [[John Kirtland Wright|John K. Wright]] still preferred ''isogram'', but it never attained wide usage. During the early 20th century, ''isopleth'' ({{langx|grc|πλῆθος|plethos|amount|label=none}}) was being used by 1911 in the United States, while ''isarithm'' ({{langx|grc|ἀριθμός|arithmos|number|label=none}}) had become common in Europe. Additional alternatives, including the Greek-English hybrid ''isoline'' and ''isometric line'' ({{langx|grc|μέτρον|metron|measure|label=none}}), also emerged. Despite attempts to select a single standard, all of these alternatives have survived to the present.<ref name="Wright1930">{{cite journal |last1= Wright |first1=John K. |title=Isopleth as a Generic Term |journal=Geographical Review |date=Apr 1930 |volume=20 |issue=2 |page=341 |jstor=208890 |url=https://www.jstor.org/stable/208890}}</ref><ref name="wright1944">{{cite journal |last1=Wright |first1=John K. |title=The Terminology of Certain Map Symbols |journal=Geographical Review |date=Oct 1944 |volume=34 |issue=4 |pages=653–654 |doi= 10.2307/210035 |jstor=210035 |bibcode=1944GeoRv..34..653W |url=https://www.jstor.org/stable/210035}}</ref>

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.