An example of d3-contour.
forked from mbostock's block: Contour Plot II
forked from anonymous's block: Contour experiment
forked from RobinL's block: Contour experiment
https://d3js.org/d3.v4.min.js
https://d3js.org/d3-contour.v1.min.js
https://d3js.org/d3-scale-chromatic.v1.min.js