“People are poor at accurately judging areas; they do much better comparing linear measures like the lengths of a bar or the heights of a point. Areas can be useful where precision’s not importantâ€â€circles can be scattered over a map, for example, to allow readers to scan for trends. But too often designers indicate data with areas because shapes are cooler than lines and you can arrange them in pretty patterns.
Regardless of the shape chosen, because we have a hard time judging areas, it’s vitally important that sizes are calculated accurately: namely, proportional to the value they represent. Otherwise the designer is telling lies.”