[Overall level questions involved an] understanding of the deep structure of the data being presented in their totality, usually comparing trends and seeing groupings.
Notes from Wikiquote
II. The properties of the graphic system
There are as many types of questions as components in the information.
The aim of the graphic is to make the relationship among previously defined sets appear.
Quote text and notes from Wikiquote: Jacques Bertin (page history), available under CC BY-SA 4.0. Source quality and labels are our own summary of what Wikiquote records.