Level 2 · Which chart answers the question?

Every chart type answers one kind of question well. Choosing starts with the question, never with the chart gallery. Say the question in one sentence, find its shape below, and the chart follows.

The question decides the chart

Question	Chart	Harbor & Pine example
Which is bigger? (compare categories)	Column or bar	revenue per category
How did it change over time?	Line	daily marketing spend
What share of one whole is each part?	Pie (few slices)	share of the day’s revenue
Do two numbers move together?	Scatter	price vs units sold per product
How are values spread out?	Histogram	how many products in each price band
Total per group and what it’s made of?	Stacked bar or column	returns per category by reason
Two measures with different scales on one picture?	Combo (column + line, second axis)	units sold and average price per product
Several items scored on several metrics?	Radar	stores compared on sales, units and rating

Stacked bars

A stacked bar puts several series end to end inside one bar. The bar’s length is the total; the segments are the parts. Use it when both the totals and the mix matter, with no more than four or five segments. Only the first segment sits on the baseline, so the middle segments are hard to compare between bars. If the mix is the real story, a 100% stacked bar sets every bar to the same length and shows shares instead. In Excel: Insert → Charts → Column or Bar → Stacked.

Combo charts

Sometimes you want two different measures on one chart, like total units sold (hundreds) and average price (tens of dollars) per product. On one axis the smaller measure would be a flat line along the floor. A combo chart draws one series as columns and the other as a line on a secondary axis on the right. In Excel: Insert → Charts → Combo, or right-click a series → Change Series Chart Type, set it to Line and tick Secondary Axis. Label both axes, because a reader can’t tell which scale a line uses otherwise.

Radar, histogram and the rest

A radar chart puts one axis per metric around a circle and draws each item as a shape. It can compare three or four stores on three or four metrics, but areas are hard to judge, and a grouped bar chart usually says the same thing more clearly. A histogram is a column chart of counts per range of values; you build one in level 4. Excel 2016 and later also have Insert → Charts → Statistic → Histogram, which picks the ranges for you.

Common mistakes

• Starting from the chart gallery instead of the question.
• A line chart across categories. Lines connect points in order, so they suggest time or sequence.
• Pies for comparison between groups. Two pies side by side can’t show which group is bigger.
• Two scales on one axis. The smaller series vanishes. Use a combo chart with a secondary axis, or two charts.