A line that defines the shape(s) of an object.
an imaginary line, or isoline, connecting points of equal elevation above some fixed level, or datum; used to represent 3D curved surfaces such as terrain
A line on a map that traces locations where the value of a variable is constant. For example, contour lines of elevation trace points of equal elevation across the map. All points on the “ten foot” contour line are ten feet above sea level.