Bar chart

Overview
A bar chart, also known as a bar graph, is a chart with rectangular bars of lengths usually proportional to the magnitudes or frequencies of what they represent. Bar charts are used for comparing two or more values. The bars can be horizontally or vertically oriented. Sometimes a stretched graphic is used instead of a solid                                                                bar.

Example
The example chart is based on the results of the election for the European Parliament in 2004 and in 1999. The following table lists the number of seats allocated to each party group. The results of 1999 have been multiplied by 1.16933, to compensate for the change in number of seats between those years.

A bar chart visualizing the above results of the 2004 election can look like this: (If all the values were arranged in descending order this type of bar graph would be called a pareto chart.)

This bar chart shows both the results of 2004, and those of 1999:

History
The bar chart is possibly the invention of the Scots engineer and economist William Playfair (1759-1823). A bar chart was used in his work The Commercial and Political Atlas (London, 1786).