# Quantitative Scales

var colorScale = d3.scale.quantile()            .domain([d3.max(dataset) / 4, d3.max(dataset) / 2 , 3*d3.max(dataset) / 4, d3.max(dataset)])            .range(["#9c9ede","#6b6ecf","#5254a3", "#393b79"]);

So the code divide the value into 4 range, if the value smaller than 1/4 max value, then it use #9c9ede color; from 1/4 - 1/2: #6b6ecf ... from 3/4 - 1: #393b79

var q = d3.scale.quantize().domain([0, 1]).range(['a', 'b', 'c']); //q(0.3) === 'a', q(0.4) === 'b', q(0.6) === 'b', q(0.7) ==='c'; //q.invertExtent('a') returns [0, 0.3333333333333333]

### use:

.attr('fill', colorScale);