A contour line of the function is a 2-dimensional curve with the equation , where k is a constant in the range of f. A contour line can be described as the intersection of the horizontal plane with the surface defined by f. Contour lines are also known as level curves.
A contour plot is a plot containing several contour lines, each representing a different magnitude of k. The contour interval is the difference in the value of between successive contour lines. The regions between contours are often shaded or colored to indicate these differences in the value of k.
In cartography, contour lines are commonly used to illustrate points of equal elevation above a given level, such as mean sea level. A contour map is a map illustrated with contour lines, the most common example of which is a topographic map that shows mountains, hills, valleys, and the steepness of slopes through contour lines representing elevation.