等雨线（英语：Isohyet），又称等雨量线，将同一段时间内降水量相同的地方相连即可形成等雨线曲线，等雨线依时间长短一般分为年雨线与日雨线等，绘制成图表及为等雨量图，等雨量图的目的即把雨量的平面分布以图像显示出来，用于观察、推测、研究等用途。

A contour line (also isoline, isopleth, or isarithm) of a function of two variables is a curve along which the function has a constant value. It is a cross-section of the three-dimensional graph of the function f(x, y) parallel to the x, y plane. In cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level. A contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness of slopes. The contour interval of a contour map is the difference in elevation between successive contour lines.