Heatmap Chart

The data format for heatmap chart per-series is similar to cartesian charts. But instead of y values they are heat values. The series names will be the y values.

{
  <x value> => <heat value>,
  <x value> => <heat value>,
  ...
}

or this:

[
  [<x value>, <heat value>],
  [<x value>, <heat value>],
  ...
]