Used for 2 or more variables; Colors, shading, and multiple displays creates a very specific story.
Present over a region or location to indicate movement or density
Reserved for single variable charting, shows how data spreads over the specified interval
Illustrates similarities and differences between the data; this type of visual utilizes the minimum, maximum, range and performance of the data to convey insights.
This enables comparisons among subcategories by evaluating relative proportions, for example, demographics by neighborhood.
Sosulski, Kristen. Data Visualization Made Simple (p. 49). Taylor and Francis. Kindle Edition.