A usual practice in data visualization consists of scaling a graphic component to a numeric value. For instance, bar lengths are scaled to values in a barplot. When the value is scaled to an area, scaling it by two sides at the same time produces a quadratic effect for a linear change. This amplifies the differences.

Example

Here is an example coming from the Barack Obama’s State of the Union speech in 2011. It shows the 2010 Gross Domestic Product of 5 countries, each value being represented by a circle. The radius of each circle has been scaled based on the size of each nation’s economy.