Reading "A History of Data Visualization and Graphic Communication", I have come across William Playfair's story behind creating line charts. It then has me thinking if I can add another layer to the line chart. Next, I have tried to read Playfair's defining work, "The Commercial and Political Atlas". Thinking back, I recall some of the blog posts that I have written about.
In a book review from 26 February 2022 on "Data Visualization Made Simple", having seen the bullet graph, I have dived deeper into the chart that is created by Stephen Few.
In a post on 22 January 2022, I have written about inspiring charts from the Economist. One of the charts is a combination chart of a warming stripe and line chart as seen below:
Putting both ideas together, I come up with a combination chart of a bullet graph and a line chart. Once again, like some ideas being shared on this blog, I do not think that I am the first to come up with this, but I think that it has not been officially documented and widely used yet. This is the bullet time:
Like how a bullet graph works, the bullet time provides a main measure in the foreground. Instead of a bar, it is a line on a time series chart. There is also a reference line for the goal to reach or any measurement, like the previous year's results or value to compare to. The background is filled with layers of different ranges that can be indicative of how well the values are (bad, normal, and good), or it can also refer to benchmarks or thresholds to pass.
As with a line chart, this adds a time dimension but in return gives up the compactness of the initial bullet graph. This allows users to know when the values have passed the different thresholds.
The bullet time can also come with multiple lines that give a view of a few items at once for comparison purposes.
All in all, this chart experiment has forced me to think about how to improve a two-century-old idea. It may have been quite difficult to do so and I do think that this idea has already been out there, but the bullet graph just has been given more focus and attention.
Postscript: Upon more research, I have found a version of line chart with bands called band charts. It seems that the bullet time is just a band chart with a target line.