this iteration uses a quantile scale with naive linear breaks to map values in the data to colors on the choropleth map
the remaining examples in this design study also use a quantile scale to map data thresholds to discrete colors.
🎩 @adamrpearce for suggesting a quantile scale over in the #help channel of the d3js slack
📄 http://roadtolarissa.com/blog/2015/01/04/coloring-maps-with-d3/
do check out the other examples in this world map series:
world map 00 original example
world map 01 fix tooltip value
world map 02 d3 v4
world map 03 es2015 + update code style
world map 04 manual breaks + threshold scale
world map 05 linear breaks + quantize scale
world map 06 linear breaks + quantiles scale
world map 07 Jenks natural breaks
world map 08 ckmeans cluster max breaks
world map 09 ckmeans cluster min breaks