Difference Chart: Purpose, Code, and Description

Purpose

A difference chart is a variation on a bivariate area chart. This is a line chart that includes two lines that are interlinked by filling the space between the lines. A difference chart is able to highlight the differences between the lines by filling the area between them with different colors, depending on which line is the greater value.

This technique harks back at least as far as William Playfair when he was describing the time series of exports and imports of Denmark and Norway in 1786.