Modern spreadsheet programs offer all kinds of chart options. Most suck.

Dr. Drang recently called out the stacked area chart. I completely agree with the good doctor that stacked area charts do a poor job of exposing trends in data.

Whenever I attempt to present data that vary with time, I always start simple—with a line chart. Yes, line charts are boring. They’ll win you few to nil artistic points.

Consider Dr. Drang’s market share data in the form of a line chart:

  <img src="/img/drang-market-share-pe.png" alt=""/>

No, it’s not obvious that the y-coordinates sum to 100 percent at each time step, but I think that’s secondary to making the trend in the data crystal clear.

I’m no cognitive psychologist, but I think the human mind naturally looks for lines in charts. Stacked area charts have a way of implying lines where they don’t really exist.

Line charts are less apt to create optical illusions because what you see is what you get. The reference point for each line is the same: the horizontal axis. There’s no question that Orange is falling, Blue is rising, and that Green is increasingly linearly.

Because trends are so immediately clear in a line chart, viewers will spend time contemplating the meaning of the trends rather than wasting mental calories decrypting the graph’s basic message. For example, questions like “why are Blue and Orange negatively correlated?” or “why does Green seem independent from the others?” become possible. Busier charts might not elicit those questions.

It’s likely that there is a more creative way to convey the same information, but I think any departure from a simple line chart should be judged against what Edward Tufte would call the line chart’s “data-ink ratio.”

In other words, as you increase your artistic license, ask: Am I adding insight or distraction?