Bubble Chart

Figure purpose

Bubble chart lets you place three numeric variables into one view by using x position, y position, and marker size. That can be useful when one extra quantity matters, but you still want to keep a scatter-like layout.

When to use or avoid

Use bubble chart when a third numeric variable adds useful context to a basic x-y relationship. It works best when the audience needs a rough visual comparison rather than precise size judgment.

Avoid it when marker size is doing too much work. Size encoding is harder to read precisely than position, and overlapping bubbles can hide small groups or edge cases.

The current product supports numeric x-y-size plotting. Docs should still avoid implying that grouped color behavior is equally mature in the rendered figure.

Required columns

• One numeric x variable
• One numeric y variable
• One numeric size variable

Optional grouping context may exist around the figure flow, but the current public page should be read as a size-encoded scatter surface first.

Related statistics or disclosure

Bubble chart is usually an exploratory or descriptive display. It should not be described as if it provides a stronger inferential summary than Scatter Plot or Regression Plot.

Alternative figures

• Use Scatter Plot when two variables are the real focus and size encoding would make the view harder to read.
• Use Regression Plot when the main question is the relationship trend rather than a third magnitude variable.
• Prefer separate panels or separate figures when the third variable is important enough that bubble size becomes difficult to compare.

TODO (Phase02+)

• Expand grouped-color guidance only if the renderer later exposes a clearer public contract for that encoding.