The idea
The question before the chart
Someone hands you a spreadsheet and says "make a chart".
You cannot. Not yet. A chart is an answer, so you need the question first: is the reader trying to compare two things, see a spread, understand a total, or rank a list?
The textbook's rule is short: understand the needs of the audience to determine the goal, understand the type of data you have, then choose. In that order.
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