Saturday, May 17, 2008

An Introduction to Bar Charts

In A Round Chart in a Square Hole - Stacked Bar Charts I described a particular type of bar chart known as a stacked bar chart, that may be used like a pie chart to display proportional data.

Bar charts can also be used as a far more general type of graphical display.

Read the following section from the OpenLearn unit More working with charts, graphs and tables: Bar Charts

What sort of data can bar charts be used to visualise? How should you decide whether to use a vertical or a horizontal bar chart?

Bar charts are particulalry effective when you want to compare the relative measures applied to discontinuous or independent categories. For example, if you wanted to compare the relative numbers of subscribers to various broadband suppliers in a particular year, you might represent each supplier by a different bar in the bar chart.

All spreadsheet packages contain wizards that let you create a simple bar chart. for example, the following Google chart is generated from a Google spreadsheet using the data described in the OpenLearn material.

As with many other chart types, a 3D representation is also possible:

It is also often possible to produce stylised bar charts - this is particularly the case in many marketing campaigns.

If you are ever tempted to use such displays, take care to choose an appropriately stylised display, and try not to make it misleading. For example, in the above case, the breaks in each bar where the coaches are coupled together can confuse the eye as it tries to judge the relative attendance proportions for each category.

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