Stephen Few, an information visualization consultant and author, designed this chart to solve some of the problems that the gauges and meters type of charts poses. Gauges, although simple to understand, take a lot of space to show only one measure. Bullet graphs are a combination of the bar graph and thermometer types of charts, and they show a measure of interest in the form of a bar graph (which is the bullet) and target variables.
Let's use the sample file Sample – Coffee Chain (Access). Open a new worksheet and select Sample – Coffee Chain (Access) as the data source.
Once the data is loaded on the sheet, perform the following steps to create a bullet graph:
- Click on the Show Me button to bring the Show Me toolbar on the screen.
- While holding the Ctrl key, click on Type and Market from Dimensions and Budget Sales and Sales from Measures.
- Click on the bullet graphs icon on the Show Me toolbar.
- Right-click on the x axis (the Budget Sales axis) and click on Swap Reference Line Fields. The final chart should look like the one in the following screenshot:
Although bullet graphs maximize the available space to show relevant information, readers require detailed explanation as to what all the components of the graphic are encoding. In this recipe, since we want to compare the budgeted sales with the actual sales, we had to swap the reference line from Sales to Budget Sales. The black bar on the graphic shows the budgeted sales and the blue bar shows the actual sales. The dark gray background color shows 60 percent of the actual sales and the lighter gray shows 80 percent of the actual sales. As we can see in this chart, blue bars crossed all the black lines, and that tells us that both the coffee types and all market regions exceeded the budgeted sales.
A blog post by Data Pig Technologies discusses some of the problems with the bullet graph. The main problem is intuitive understanding of this chart. You can read about this problem and the reply by Stephen Few at http://datapigtechnologies.com/blog/index.php/the-good-and-bad-of-bullet-graphs/.