Hexbin

'chart-types-hexbin': () => ({
  rows: [], config: {},
  foot: ['thousands of points binned into hexagons', 'the darker the cell, the more points fell in it'],
  mount: mountGridCharts({
    rows: book(5_000), columns: bookCols, columnsPer: 1, chartHeight: 360,
    chartTypeModules: ['hexbin'],
    charts: [{ type: 'hexbin', x: 'volume', y: 'notional', title: 'Notional against volume' }],
  }),
}),