- Don't force an Area chart. Line charts are often the more legible option.
- Help your consumers with consistent reference marks
- The most powerful aspect of an area chart is it's ability to give a total, but this can distract from the individual variables.
Area charts emphasize the combined performance of a cohort rather than it's individual pieces. If that is your key takeaway to an audience, then an Area chart can be put to good use. However Area Charts often put too much onus on the end users while offering some pretty subtle weaknesses which make it, in my opinion, one of the more challenging charts to effectively use.
Here’s an area chart of total volume of alcohol sold in Canada from 2002-2016
It’s showing the growth of three common alcoholic beverage types (+ other which is coolers, ciders etc) from 2002 – 2016.
At a glance we can tell that total consumption has increased since 2002, having plateaued a bit between 2009 and 2014. We can see that Other is quite obviously the lowest type and beer is the highest.
At a glance, that may be the only things we can say for certain based on this one view.
Let’s quickly compare this to a line chart showing the same information.
The line chart, in this circumstance, drives your attention to some of the big stories. Wines have closed a big gap on spirits. We can also see there's been a slight uptick in Other, and Beer isn't growing much at all. This offers a much deeper analysis than the Area chart. You can also see that all sectors are growing, which leads you to conclude that the industry is growing.
When to actually use Area Charts
Area charts start to add value if you're forced to compare many variables. Take a look at the beer by province chart below. It's showing a lot while being just shy of too busy. You can quickly see that:
Ontario has 65% of Beer sales
British Columbia, Quebec and Ontario make up 75% of Beer Sales
It also shows the relative insignificance of size from the maritimes and territories (despite our best efforts).
This becomes total chaos on a line chart, which has a bunch of clutter, shows the smaller provinces as dwarfed by the bigger players and, overall, is a big mess. .
Let's take the scenario one step further. Let's now compare Provincial Sales of all alcohol side by side
The area charts, side by side, give a lot of interesting information. They all use the same scale and with the reference lines following from one to the other it's easy to have a dialogue with this chart. Look at the jump for Quebec Wine compared to Saskatchewan who drops off completely.
How about the higher variability of "other" which sees significantly more peaks and troughs than the other types.
What's most interesting is the amount of information you can convey with this in a relatively small space. The impact of each mark means that you can get more with less to tell the story.
Most importantly is what this doesn't tell. There's no way to compare total volume by type from province to province. You don't know year of year growth in any of these provinces. The Area chart forces a certain narrative, and it's necessary to determine if the chart matches the message (which is a great rule of thumb).
Area charts are so frequently included in my rough sketches of dashboards and then fail to make the final cut. They unfortunately don't have a wide range of use cases that can't be better done by line or stacked bar charts. But if you can find the right place to intuitively use one they can be a powerful accent in your analysis.
I've created a full dashboard if you're interested in diving into this information further. It is best viewed on my Tableau Public Site