Have you ever looked at a visualization and think, “How’d they do that?” I know I have.
So much like the Tableau podcast I used to co-host, I decided that I would find out, put it in my own words, and share out on my blog so I remember how to create them later because my memory .
So for my first HTDT, I was looking at the Workout Wednesday site and found the comet chart challenge. I was more interested in the how’d they do that than meet the specific requirements that were outlined. So off to google I went and that’s where I found Steve Wexler’s blog on comet charts.
For a minute, I thought I might just make the chart following Steve’s directions (his screenshots are on point), point to his blog, and call it a day. However, you know how it makes more sense when you put it in your own words? So I decided to reserve engineer this Comet Chart from a few of the screenshots.
Why’d they do that?
Before I get into the HTDT, I want to share why you’d use a comet chart. It’s an alternative to side-by-side data comparison for two time periods. Is a good alternative? Well, that’s up to your audience.
Here are some pros and cons of a comet chart:
Pros
– Creates space in the visualization
– Alleviates bar chart burnout
Cons
– Might confuse the audience by making them think more about the visualization as opposed to comprehending the data.
– Might be inaccessible. Heads or tails might cover up other data points, which goes against the “visual elements need to be visually distinguishable” aspect of WCAG guidelines.
How’d they do that?
Build your base
1. Drag your measure onto columns (in this case, I used Sales). Drag dimension (sub-category) to rows.
2. Filter for two time periods that you’re interested in.
The base in this case is a bar chart.
Make the adjustments
3. Change the mark type from automatic to line.
4. Add your time data item (Order Date) to size and to path.
Side note: You might look at yours compared to the final product and think, this looks cool, but why doesn’t mine look like a comet?
5. As needed, align time periods. Notice in the image above, that Order date is listed as Quarter (Order Date) on the size card. It needs to be at the same level as the rest of the time period (all years or all quarters).
6. Format to help the your audience easily understand the data.
And that’s how they did it!
