Number & MeasureGreek → English
Isopleth
/ˈaɪsəplɛθ/noun
A line on a map or chart joining points of equal value for some quantity.
The Greek roots
ἴσος
ísos
equal
πλῆθος
plêthos
quantity, multitude
Literally: “equal quantity”
The story of the word
The general term for a whole family of lines that mapmakers otherwise name one by one: isobar for pressure, isotherm for temperature, isohyet for rainfall, isochrone for travel time. The technique goes back to Halley's 1701 chart of magnetic variation, which is usually counted the first published isoline map. Contours on a walking map are isopleths of height.
- How it travelled
- Ancient Greek → scientific coinage → English
- First recorded
- 19th century
Same family
isobarisothermisoscelesplethora
In a sentence
The isopleths bunch where the gradient steepens.
Label every fifth isopleth or the map becomes unreadable.