Monotone cubic interpolation

Monotone cubic interpolation is a way of drawing a curved line through a set of points such that the curve will always go up or down between the points but never change direction quickly. Think of it like drawing a gentle series of steps connecting each point. You might use this when you want to draw an exact line between a set of points, but you want it to be smooth and curved, instead of with a lot of drastic changes in direction.