In the past three weeks, we’ve been running a series on the tweaks that designers do to charts to make them fit the aesthetics of the graphics they are creating. So far, we showed you some of the ways designers get creative with pie charts, bar charts and area based encodings. Line charts also get tweaked by designers, with varying degrees of detriment to their communicativeness. Let’s take a look at five ways designers use line charts, and dissect if and how they are harming the communication of the data.
- Curved Lines are one of the most common ways that designers change line charts. The added interpolation on the charts can help to make a chart with sharp peaks and valleys easier to read, but it also makes the resolution of the data look higher than it actually is. This can be misleading and make it look to the viewer as though the data series is doing better or worse than it actually is. Be very careful with this technique.
- Thick Lines definitely emphasize data, but they can also make it more difficult to determine what the actual value of the data point is. This effect is exasperated by angular connections between line segments, rather than radiused corners. Keep your line weights at a reasonable size.
- Gradient Coloring is a neat effect, and it is generally considered a good thing, as it produces a double encoding of the data. This means that looking at the color of the line can provide the same data as looking at the vertical position. And, best of all, you don’t even need a color scale because the scale is built into the chart already.
- Dashed Lines are potentially dangerous territory. First of all, typically a line chart means there is continuity in the data series, and introducing dashes indicates discontinuity. This nitpick aside, though, the frequency and length of the dashes matters. If the dashes keep the salient points of the line (the actual data points) from being drawn, this can be a bad technique.
- Points are typically a pretty good thing on line charts. They help to anchor the actual data locations, and they help to communicate that although the represented value is continuous, it is still only sampled discretely.
- Icon Metaphors on line charts are the type of aesthetic intervention (chart junk) that help the viewer to remember and understand the data they are looking at. This technique is fun and playful, has minimal impact on the data while making the chart more memorable.
Along with these aesthetic considerations, it is important to use proper gridlines, and include the appropriate context on the axes of the charts. Well designed line charts can be extremely effective at communicating data, which may be why they are one of the oldest charts around. Drew Skau is Visualization Architect at Visual.ly and a PhD Computer Science Visualization student at UNCC with an undergraduate degree in Architecture. You can follow him on twitter @SeeingStructure