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Selecting the Right Charts and Indicators for Visually Impactful Dashboards
Part 3 of 4 - Displaying Two Data Elements in a Single Chart

by Frank Smietana, BI Specialist, Dimensional InsightTuesday, December 7, 2010

Today’s dashboard environments provide developers with a rich set of indicators and charts, ranging from bullet graphs to sparklines and bar charts to bubble graphs. Additionally, numerous formatting options such as splines and 3D displays are available, adding even more complexity. To the casual observer, chart types and options may appear to be largely interchangeable and are simply left to the discretion of the developer. But as the art and science of effective dashboard design has evolved, data visualization gurus have established some guidelines regarding which charts and indicators to use for various types of data and how to present those charts most effectively. This issue is receiving increasing media attention as dashboards migrate to the limited display “real estate” found on mobile devices, placing a premium on efficient dashboard based information delivery.

In this series of Dashboard Insight articles we’ll look at some popular chart types and describe how to use them most effectively in your dashboards, as well as pitfalls to avoid. In Part 1, we’ll discuss effective dashboard indicators. Part 2 will deal with basic charts and in Part 3 we’ll move on to charts that display more than one data element. In our final article, we’ll present some special purpose charts. With this collection of indicators and charts, your dashboards will stand head and shoulders above the competition, and leave your users with an unambiguous and actionable view of their data.

Part 3 - Displaying Two Data Elements in a Single Chart

Basic charts such as Bar, Line, Point, and Bubble charts can be adapted to display the intersection of two data elements. The following three charts display revenue for the dual elements of fiscal Quarter and Salesperson. If your end user is more interested in intra-quarter comparisons between sales people, the Bar chart is the clearest representation. On the other hand, the Line chart does a better job of illustrating quarter to quarter revenue variations for each Salesperson. The Point chart is the least desirable option, because several data points are hidden underneath others. The Point chart does however provide the clearest display of Salesperson ranking within each Quarter.

Bar Graph
Line Graph
Bubble Chart

A Bar Stack chart is another way to encode two data elements in a single graph. In this example, Product Family is represented by the labels on the x-axis while the colored columns represent the Sales Region. Staggering the x-axis labels instead of displaying them at an angle makes the graph far more readable. At a glance, dashboard users can see that the biggest revenue generators are Butter, Cheese, Ice Cream and Milk, while Cottage Cheese and Cream Cheese are underperformers.

Stacked Bar Graph

But what if we are more interested in gaining a clearer picture of the revenue each Sales Region contributes to the individual Product Families? A variation called a Percentage Bar Stack chart can be used. The y-axis now describes percentage of revenue rather than absolute dollars amounts. Knowing which view of the data your users are interested in helps to choose the right chart style.

Just like Linear Bubble charts, the Bubble Cross-plot uses the bubble diameter to display an additional quantitative metric, in this case Units Sold.

cross-plot bubble chart

In next week’s edition of Dashboard Insight, we’ll present some additional charts that you can incorporate into your dashboards to maximize the information content of certain types of data.

About the author

Frank Smietana is a Senior Technical Writer at Dimensional Insight, headquartered in Burlington, Mass.

For more information please visit Dimensional Insight

To download the complete four part series click here.

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