noun
isopleth; isogram; isoline; contour line
Technical term in geography, meteorology, and statistics for a line connecting points of equal value on a map or chart.
天気図には気圧の等値線が引かれている。
Isobars, which are isopleths of atmospheric pressure, are drawn on the weather map.
この地図の等値線は標高を示している。
The contour lines on this map indicate elevation.
等温線 is an isotherm (line of equal temperature), a specific type of 等値線.
Compound of 等 (equal) + 値 (value) + 線 (line). A modern technical term likely coined as a calque of Western scientific concepts such as 'isopleth' or 'isoline'.