Scatter Plot (XY Plot)

A scatter plot places two metric characteristics against each other: every value pair becomes a point. It answers whether an association between X and Y exists, in which direction, how tight it is, and whether it stays the same across the range.

• Direction — a rising or falling cloud of points
• Form — linear, curved or stepped; only the linear case is captured correctly by correlation
• Tightness — how narrow the band containing the points is
• Anomalies — outliers, clusters, gaps and a widening band (heteroscedasticity)

Encoding a third numeric column through point size turns it into a bubble chart. The size must be scaled by area — the diameter follows the square root of the value, because the eye reads area, not radius, as quantity.