Spark lines are an idea from Edward Tufte, author of books such as Envisioning Information. The concept of a spark line is simplicity itself – take a line graph and delete everything but the line itself. This enables you to present a big chunk of information in a very small space, perfect for dashboards. Take the following example:
This is fairly typical of a dashboard or scorecard used to present key performance indicators (KPIs). You’ve got the sales figure, a green light and an arrow going in the right direction. Sales must be good! But how much information do you really have here? You know that your sales number is in a good position today, and compared to your last measurement it is going in the right direction. What does that information really tell you?.
Let’s use a sparkline instead:
The spark line enables you to present a far bigger range of figures with minimal extra space. When you use the traffic light and arrow, you can only see the last two points on this line. But now you can potentially see a whole year’s worth of data. And what does this spark line tell you? That sales are currently good and going in the right direction, but the pattern through the year looks very erratic. Who knows what next month’s figures will look like. Why is that? Can anything be done to settle into a growth curve or are the causes all external and out of your control? Are your suppliers letting you down, disrupting your production line? The spark line encourages you to investigate, providing you with an opportunity to be proactive in resolving issues. Traffic lights create a reactive approach – you only start to investigate when they go red or the arrow is already pointing in the wrong direction.
Bullet graphs are an idea from Stephen Few, providing an alternative to the popular dashboard tool – gauges. Another example:
This is a classic gauge, displaying a measure and the range of values that indicate where you would like it to be. In this case, customer satisfaction is healthily in the green at above 75%. But again, how much information have you been given? A measure and where it sits within a range. That gauge takes up an awful lot of screen estate to give you so little. Enter the bullet graph:
A bullet graph is the perfect diet – it slims down a gauge and gives you extra value to boot. Styled like a thermometer, you can still see the range of values, but now a simple line indicates your current measure. But in addition, the horizontal line can provide a clear alternative measure (this is harder to do with the gauge, where it ends up looking like half a clock). That horizontal line might represent last month’s figure, or could represent the target. Either way, you now have a comparative measure.
To put these two ideas together, it’s worth comparing two dashboards to demonstrate how much or how little information is often presented:
Here is a classic dashboard, with lots of pretty graphs and charts. But, before you even figure out what it all means, how much does it really tell you? Now let’s look at an example that uses spark lines and bullet graphs:
Before you even start to interpret what this dashboard contains, you can see a lot more information is available in a format that you can analyse. And now let’s take it a stage further… Let’s take that dashboard out of the browser…
This screenshot is Excel – your good ol’ spreadsheet (and it’s not even the latest version at that). This simple screen of data inside Excel contains more useful information than I’ve seen in far more complex and expensive business intelligence tools.
How do you create a spark line in Excel? Simple – just create a normal line chart and delete out everything other than the line (go into Chart Options, delete the grid lines, the axis, the heading, the background, everything!).
The screenshots above are all available over on The Dashboard Spy’s web site, a blog I recommend you subscribe to if you are interested in this subject. Having read Stephen Few’s book, it is great fun to critique the different dashboards on display there. I was going to create my own examples in Excel, but others beat me to it and I’m all for not reinventing the wheel. I’ll use a later post to explore if/how Excel 2007’s new data visualisations can enhance dashboards… …and since starting this post, The Dashboard Spy has beaten me to it again.
If you are tasked with designing a dashboard or scorecard, there is one important question you should always ask the audience who will be using the end result. Is the dashboard being designed to provide quick answers or prompt for more questions? Too often, the answer is the former when it should be the latter but that’s a whole different political question 🙂 Let’s just focus on designing for the desired role…
Going back to the first image – the sale figure with a green traffic light and an arrow going upwards. That is a classic ‘answer’ KPI. Are my sales good? Yup! Are they going in the right direction? Yup! Great! I can move on to the next task. If that really is all the audience wants to know, then stick with the colourful images and minimal content. The irony is, dashboards that provide quick answers are largely redundant any way. Quick answers are answers you already know and just want validated. If you are interested in sales, you are going to know if the company is doing well or not before you even look
at that dashboard. Just walk down the corridor, lurk by the water cooler, linger in the toilet even – you’ll know from the atmosphere within the office if your sales are good or not. It won’t necessarily tell you whether they are going to stay that way…
The spark line is far more suited to the valuable use of a dashboard – to prompt proactive investigations when the numbers may be good but don’t look quite right…
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