Editing Contour line (section)

=== Isopleths ===<!-- [[Isopleth]] and [[Isopleths]] redirect here -->
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 a point; this distinction has since been followed generally.<ref name="wright1944" /><ref>{{cite journal | vauthors = Robinson AH | author-link = Arthur H. Robinson | year = 1971 | title = The genealogy of the isopleth | journal = Cartographic Journal | volume = 8 | issue = 1 | pages = 49–53 | doi = 10.1179/caj.1971.8.1.49 | bibcode = 1971CartJ...8...49R }}</ref> An example of an isopleth is [[population density]], which can be calculated by dividing the population of a [[census tract|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 a [[choropleth map]].<ref>T. Slocum, R. McMaster, F. Kessler, and H. Howard, ''Thematic Cartography and Geographic Visualization'', 2nd edition, Pearson, 2005, {{ISBN|0-13-035123-7}}, p. 272.</ref><ref>ArcGIS, [http://www.arcgis.com/home/item.html?id=830338fc8ca947c38b8d97f51724f5c9 Isopleth: Contours], 2013.</ref>

In meteorology, the word ''isopleth'' is used for any type of contour line.<ref>NOAA's National Weather Service, [http://w1.weather.gov/glossary/index.php?letter=i Glossary].</ref>