Contour plots draw lines to represent levels between surfaces. As with other 3D representations, we now need three variables, x, y, and z, and speaking for ggplot2
, data frame must display a single row for each unique combination of x and y. That is why it's easier to bring these visuals by applying 2D kernel density estimations -- there is a single row for each unique combination of x and y.
This recipe will demonstrate a very easy way to create and plot those estimates by drawing contour plots with ggplot2
. We will be using variables speed
and dist
from car
data frame to draw this plot. Recipe highlights the very basics of making a contour plot understandable while it teaches how to improve this visual by drawing filled polygons instead of empty curves.