Bubble chart

Bubble charts can facilitate the understanding of social, economical, medical, and other scientific relationships.

The human visual system most naturally experiences a disk's size in terms of its diameter, rather than area.

And because many people are unfamiliar with—or do not stop to consider—the issue and its impact on perception, those who are aware of it often have to hesitate in interpreting a bubble chart because they cannot assume that the scaling correction was indeed made.

It is therefore important that bubble charts not only be scaled correctly, but also be clearly labeled to document that it is area, rather than radius or diameter, that conveys the data.

For example, the maximum bubble size is often set to some fraction of the total width of the chart, and therefore will not equal the true measurement value.

As a fallback, some users of bubble charts resort to graphic symbology to express nonpositive data values.

To represent zero-valued data, some users dispense with disks altogether, using, say, a square centered at the appropriate location.

Additional information about the entities beyond their three primary values can often be incorporated by rendering their disks in colors and patterns that are chosen in a systematic way.