Bubble Chart Size Legends for Affiliate Campaign Reports

A third measure needs its own explanation

Performance marketing media buying reports sometimes use bubble charts to compare three campaign measures at once. Horizontal and vertical positions encode two measures, while bubble size encodes a third. Without a clear size legend, readers may mistake a visually prominent campaign for the best-performing one. This proposed reporting review addresses interpretation rather than recommending a particular charting platform.

Name all three measures

State the horizontal metric, vertical metric, and size metric beside the chart. Include units, date range, and the reporting basis. A campaign chart might place spend on one axis, approved commission on the other, and approved orders in bubble size. Do not allow the title to imply profitability if costs outside media spend are excluded.

Verify whether size means area or diameter

Inspect the chart configuration or ask the report owner how values become visible circles. If area represents the measure, doubling the value should double the area rather than the diameter. A hypothetical bubble for 100 orders would have twice the area of a bubble for 50 orders; its diameter would be about 1.41 times as large. Doubling diameter instead creates four times the area and can exaggerate the difference.

Include reference circles that match the encoding

Provide a few labeled size examples using the same scale as the plotted bubbles. Check that exported slides and dashboard screenshots retain the legend. If minimum bubble sizes are imposed to keep small observations visible, disclose that choice because the smallest circles may no longer support precise visual comparison. Provide a table when exact values matter.

Account for overlap and missing observations

Large bubbles can hide small ones at similar coordinates. Check the underlying campaign count against the visible chart and use labels, transparency, or separate views when needed. Define what happens to zero, negative, or missing values for the size measure. Do not silently convert missing data into a zero-sized circle and then conclude that the campaign generated no activity.

Use the view to frame a decision

For media buying teams, a bubble chart can identify campaigns that deserve closer inspection. Budget decisions still require offer terms, conversion maturity, costs, and uncertainty. Attach the values behind any highlighted campaign so an advertiser or affiliate can reproduce the comparison. A readable chart supports a discussion; it does not establish why one campaign performed differently.