noun
A line on a weather map connecting points of equal atmospheric pressure.
天気図で等圧線が混んでいる所は風が強い。
Where isobars are close together on a weather map, the wind is strong.
等圧線の間隔が広
When isobars are widely spaced, the weather becomes calm.
Weather map: the chart on which 等圧線 are drawn.
Compound of 等 (equal) + 圧 (pressure) + 線 (line), a straightforward technical term.