This is the
density 2d
section of the gallery. A 2d density represents the combined
distribution of __two quantitative variables__. If you want to know
more about this kind of chart, visit
data-to-viz.com. If you're looking for a simple way to implement it in d3.js, pick
an example below.

main density 2d types

A 2d density chart allows to visualize the
__combined distribution__ of two quantitative variables. The
concept is always the same: one variable is represented on the X axis,
the other on the Y axis. Then, the number of observations within a
particular area of the 2D space is counted and represented by a color
gradient.