IPA: /ˈaɪsəˌplɛθ/
KK: /ˈaɪsəˌplɛθ/
A line on a map or graph that connects points with the same value of a certain measurement, like temperature or pressure.
The meteorologist used an isopleth to show areas of equal rainfall on the weather map.
Isopleth is formed from "iso-" (meaning equal) and "pleth" (from Greek "plethos", meaning quantity or fullness). The term refers to a line on a map connecting points of equal value, such as temperature or elevation, thus representing equal quantities across a geographic area.
Think of 'equal' ('iso-') quantities being represented on a map by lines, which is what an isopleth does.