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A contour line or isoline connects points on a map that are of equal value. Examples of contour lines or isolines are isobars (pressure) and isotherms (temperature).

Perhaps the prototypical example of a contour line is that which connects points of equal elevation (that is, height above sea level). These are usually referred to simply as contour lines. Is there however an "iso-" name for such contour lines?

Wikipedia suggests isohypse. I don't know what exactly this is, but Wiktionary suggests that this is not quite correct--isohypse refers instead to "A line on a map connecting points of both equal height and equal barometric pressure".

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Not isomorphic, which would mean the lines connected points of the same form. Elevation is an attribute independent of form. –  Joan Pederson Mar 5 at 21:22
    
I can tell you that hypse is probably derived from the Greek ύψος (ipsos) which means height but I have no idea if the word even exists in English, let alone how it is used. –  terdon Mar 5 at 21:31
    
Well the top Google hit for isohypse says that "An isohypse, or height contour, represents the distance from zero geopotential meters." So isohypse is probably not what I'm looking for. theweatherprediction.com/habyhints/76/ –  Kenny LJ Mar 5 at 21:33
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I suggest iso-high. Because it is a pun. –  Oldcat Mar 5 at 22:16
    
To a first approximation, there is no such word, for the simple reason that contour line means a line representing the horizontal contour of the earth's surface at a given elevation. OP's assumption that isoline/isopleth and contour line are synonymous is simply incorrect. The latter are a specific subset of the former. –  FumbleFingers Mar 5 at 23:42

3 Answers 3

The Ordnance Survey, has been Britain's leading map-maker since 1791. It produces maps to the highest international standard and has the whole of the UK mapped to a scale of 1:500, with contour lines at 0.5 metre intervals.

They are called 'contour lines' and as far as I am aware they have never deviated from this nomenclature.

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Similarly, the US Geological Survey, the government mapping authority, uses topographic contour lines and bathymetric contour lines, both routinely shortened to contours. –  bib Mar 5 at 21:42
    
The question was not whether contours or contour lines was the prevalent name for this sort of map symbol, but whether there was a term for it that began iso-. –  Joan Pederson Mar 12 at 19:30

Isohypse is correct. It means equal or uniform (iso-, from Greek iso, isos: equal) height (hyps, from Greek hupsos: height or top). The study of the topography of the earth's surface, particularly its varying elevation, is hypsography. The practice of determining elevation points is hypsometry. The colors of an elevation map are called hysometric tints (may I say what a joy it has been to work for more than 20 years with cartographers who use that expression routinely?), and such a map itself is formally termed a hypsometric map. Because that term is obscure, most such maps are called topographic, elevation, or simply physical maps. Topographic maps, by the way, are any that convey the surface features of the map area, whether with contour lines, hypsometric tints, relief shading, pictographic symbols, or any other means.

Found the citations for isohypse itself; also recasting references for the related terms since the original format made them easily misunderstood.
isohypse Longman Dictionary of Geography, Audrey N. Clark, 1985 (London: Longman) and Glossary of Geology, American Geological Institute, 1972 (Washington, D.C.: American Geological Institute).
hypsometry and hypsography American Heritage Dictionary of the English Language, 4e, 2000 (Boston: Houghton Mifflin).
hypsometric map GIS Dictionary, Esri
hypsometric tints "The Development and Rationale of Cross-blended Hypsometric Tints," T. Patterson and B. Jenny, in Cartographic Perspectives, Number 69, 2011.

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Can you give a cite? –  bib Mar 5 at 21:39
    
And yes, @WS2, "isohypse" itself is esoteric, hence its absence from maps published by the Ordnance Survey, the U.S. Geological Survey, and nearly every other publisher of contour maps. I was several years into postgraduate work in geography before I encountered it, pursuing the same line of thought expressed in the original question. –  Joan Pederson Mar 5 at 21:40
    
(1) I do not have handy access to the AHDEL, 4e, but if you search for "isohypse" on ahdictionary.com, it says "No word definition found". (2) Same when I searched on the GIS Dictionary - "Sorry, isohypse was not found." (support.esri.com/en/knowledgebase/Gisdictionary/browse) (3) Nowhere does the word "isohypse" appear in the lattermost article you cite (Patterson and Jenny, 2011). –  Kenny LJ Mar 5 at 22:22
    
Wikipedia (OP's reference) has: "Contour line" is the most common usage in cartography, but isobath for underwater depths on bathymetric maps and isohypse for elevations are also used. –  Edwin Ashworth Mar 5 at 22:58
    
There are a few English texts in Google Books clearly using isohypse to mean a line connecting points of equal elevation. But the vast majority of indexed entries seem to be in German or French. Also note this text, saying isohypse ... line drawn on a map to join places where the thickness of a given atmospheric layer is the same. It's not really worth OP taking this one on board. He'd do better to alter his mistaken opinion on what "contour line" means. –  FumbleFingers Mar 5 at 23:50

Generally speaking, a line that connects 2 equal values can be considered an isoquant.

. . . An isoquant (derived from quantity and the Greek word iso, meaning equal) is a contour line drawn through the set of points at which the same quantity of output is produced while changing the quantities of two or more inputs

from Wikipedia.org

While I realize this is typically an economic term, I don't see anything preventing it from being used in other applications.

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