Bubble Chart

When to use

Bubble charts extend scatter plots with a third dimension encoded as the radius of each marker. They work well for:

Comparing entities on three numeric axes simultaneously (e.g. revenue, growth, market size).
Showing proportional quantities that don’t fit neatly on an axis.

Use ax.Bubble(xs, ys, sizes, chart.BubbleStyle{...}). All three slices must have equal length.

Basic example

GDP vs life expectancy vs population for eight major economies — the classic bubble chart. Bubble area encodes population size.

package main

import (
	"github.com/goplotlib/goplotlib/chart"
	"github.com/goplotlib/goplotlib/plot"
)

func main() {
	// Countries: USA, China, Germany, Japan, India, UK, France, Brazil
	gdp     := []float64{27.4, 17.7, 4.5, 4.3, 3.7, 3.1, 2.9, 2.1} // $ trillion
	lifeExp := []float64{78.2, 77.7, 83.6, 84.0, 69.7, 81.2, 82.6, 75.1} // years
	pop     := []float64{333, 1411, 84, 124, 1428, 68, 68, 215} // millions

	fig := plot.New(plot.WithWidth(860), plot.WithHeight(480))
	ax := fig.AddAxes()
	ax.Bubble(gdp, lifeExp, pop, chart.BubbleStyle{
		Label:   "country",
		Opacity: 0.7,
		SizeMin: 5,
		SizeMax: 40,
	})
	ax.SetTitle("GDP vs Life Expectancy (bubble = population)").
		SetXLabel("GDP ($ trillion)").
		SetYLabel("Life expectancy (years)")
}

Bubble chart

Size scaling

SizeMin and SizeMax map the raw sizes values linearly to pixel radii in [SizeMin, SizeMax]. Larger bubbles are drawn first so smaller ones are never hidden behind them.

ax.Bubble(gdp, lifeExp, pop, chart.BubbleStyle{SizeMin: 4, SizeMax: 40})

Per-point labels

Pass a Labels slice to draw a text label centered inside each bubble. Labels are automatically skipped for bubbles that are too small to fit the text.

package main

import (
	"github.com/goplotlib/goplotlib/chart"
	"github.com/goplotlib/goplotlib/plot"
)

func main() {
	gdp  := []float64{65, 48, 42, 38, 55, 12, 8, 18, 72, 52, 35, 5}
	life := []float64{79, 83, 81, 77, 82, 68, 63, 72, 82, 81, 75, 64}
	pop  := []float64{330, 125, 83, 67, 25, 1400, 215, 145, 8, 38, 210, 120}
	labels := []string{
		"USA", "Japan", "Germany", "France", "UK",
		"China", "Brazil", "Russia", "Switz.", "Spain", "Mexico", "Ethiopia",
	}
	fig := plot.New(plot.WithWidth(860), plot.WithHeight(480))
	ax := fig.AddAxes()
	ax.Bubble(gdp, life, pop, chart.BubbleStyle{SizeMin: 8, SizeMax: 50, Labels: labels})
	ax.SetTitle("GDP per Capita vs Life Expectancy vs Population").
		SetXLabel("GDP per Capita ($k)").SetYLabel("Life Expectancy (years)")
}

Bubble chart with labels

Style reference

chart.BubbleStyle fields:

Field	Type	Default	Description
`Label`	`string`	`""`	Series label shown in the legend
`Color`	`color.Color`	palette	Override the automatic palette color
`Opacity`	`float64`	`1.0`	Overall series opacity (fill capped at 0.65)
`SizeMin`	`float64`	`4`	Minimum pixel radius for bubbles
`SizeMax`	`float64`	`30`	Maximum pixel radius for bubbles
`Labels`	`[]string`	`nil`	Per-point labels drawn inside each bubble; skipped when the bubble is too small

Histogram Heatmap