These charts emphasise simple size comparisons. These can be relative comparisons (just being able to see larger/bigger) or absolute (the need to be able to see fine differences). These types of charts very often show a “counted” number of things (for example, barrels, dollars or people) – but can also be used with a wide range of data.
Smith, Alan. How Charts Work (pp. 29-30). Pearson Education. Kindle Edition.