Contour line

A contour line (also isoline, isopleth, isoquant or isarithm) of a function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value to the state. It is a plane section of the three-dimensional graph of the function f(x,y){\displaystyle f(x,y)} parallel to the (x,y){\displaystyle (x,y)}-plane. More generally, a contour line for a function of two variables is a curve connecting points where the function has the same particular value.