Reading a shot chart: zones, dots and shading
Data visuals
How to tell a hot zone from a small sample, and why the darkest patch on the chart is often the least useful shot.
A shot chart is a map of where attempts were taken, with makes and misses distinguished by colour or shape. The simplest version plots every shot as a dot. The more common version divides the half court into zones and shades each one by how the team performed there relative to an average. Both answer different questions, and confusing them is the usual mistake.
Dot charts are good for location and terrible for judgement. They show you that a player took eleven shots from the left wing and two from the right, which is real information about habit and handedness. They cannot tell you whether eleven shots is enough to mean anything. A player who makes both of his right-wing attempts is not a right-wing specialist.
Zone charts fix the sample problem by grouping, then introduce a new one: the zones are arbitrary. A shot from just inside the arc and one from just outside it land in different buckets despite being a foot apart and almost equally difficult. Since one is worth three points and the other two, the chart often shades the shorter shot red and the longer one green, which is correct on value and misleading on difficulty.
The darkest, hottest patch on almost every chart is the restricted area under the basket. That is not a finding. Everybody shoots well from two feet. What you want from a chart is the comparison against the expected rate for that zone, which is why the better ones shade by difference from average rather than by raw percentage.
Pay attention to empty space. A chart with nothing between ten and twenty feet is describing a modern offence that has deliberately removed the long two-point shot. A chart with a thick band there is either describing an older style or a player who gets forced into it by defenders going under screens. The gaps carry as much meaning as the clusters.
One habit makes charts far more useful: look at volume and efficiency together, never separately. A zone that is shaded well but contains six attempts across a season is noise. A zone shaded slightly below average that contains four hundred attempts is where the points actually came from, and it is the one a coach would change first.