Deconstructing graphics as an analysis tool in dataviz
Apr 20, 2023
One of the useful exercises I like to do with charts is to "deconstruct" them. (This amounts to a deeper version of the self-sufficiency test.)
Here is a chart stripped down to just the main visual elements.
The game is to guess what is the structure of the data given these visual elements.
I guessed the following:
- The data has a top-level split into two groups
- Within each group, the data is further split into 3 parts, corresponding to the 3 columns
- With each part, there are a variable number of subparts, each of which is given a unique color
- The color legend suggests that each group's data are split into 7 subparts, so I'm guessing that the 7 subparts are aggregated into 3 parts
- The core chart form is a stacked column chart with absolute values so relative proportions within each column (part) is important
- Comparing across columns is not supported because each column has its own total value
- Comparing same-color blocks across the two groups is meaningful. It's easier to compare their absolute values but harder to compare the relative values (proportions of total)
If I knew that the two groups are time periods, I'd also guess that the group on the left is the earlier time period, and the one on the right is the later time period. In addition to the usual left-to-right convention for time series, the columns are getting taller going left to right. Many things (not all, obviously) grow over time.
The color choice is a bit confusing because if the subparts are what I think they are, then it makes more sense to use one color and different shades within each column.
The above guesses are a mixed bag. What one learns from the exercise is what cues readers are receiving from the visual structure.
Here is the same chart with key contextual information added back:
Now I see that the chart concerns revenues of a business over two years.
My guess on the direction of time was wrong. The more recent year is placed on the left, counter to convention. This entity therefore suffered a loss of revenues from 2017-8 to 2018-9.
The entity receives substantial government funding. In 2017-8, it has 1 dollar of government funds for every 2 dollars of revenues. In 2018-9, it's roughly 2 dollars of government funds per every 3 dollars of revenues. Thus, the ratio of government funding to revenues has increased.
On closer inspection, the 7 colors do not represent 7 components of this entity's funding. The categories listed in the color legend overlap.
It's rather confusing but I missed one very important feature of the chart in my first assessment: the three columns within each year group are nested. The second column breaks down revenues into 3 parts while the third column subdivides advertising revenues into two parts.
What we've found is that this design does not offer any visual cues to help readers understand how the three columns within a year-group relates to each other. Adding guiding lines or changing the color scheme helps.
Next, I add back the data labels:
The system of labeling can be described as: label everything that is not further broken down into parts on the chart.
Because of the nested structure, this means two of the column segments, which are the sums of subparts, are not labeled. This creates a very strange appearance: usually, the largest parts are split into subparts, so such a labeling system means the largest parts/subparts are not labeled while the smaller, less influential, subparts are labeled!
You may notice another oddity. The pink segment is well above $1 billion but it is roughly the size of the third column, which represents $250 million. Thus, these columns are not drawn to scale. What happened? Keep reading.
Here is the whole chart:
A twitter follower sent me this chart. Elon Musk has been feuding with the Canadian broadcaster CBC.
Notice the scale of the vertical axis. It has a discontinuity between $700 million and $1.7 billion. In other words, the two pink sections are artificially shortened. The erased section contains $1 billion (!) Notice that the erased section is larger than the visible section.
The focus of Musk's feud with CBC is on what proportion of the company's funds come from the government. On this chart, the only way to figure that out is to copy out the data and divide. It's roughly 1.2/1.7 = 70% approx.
The exercise of deconstructing graphics helps us understand what parts are doing what, and it also reveals what cues certain parts send to readers.
In better dataviz, every part of the chart is doing something useful, it's free of redundant parts that take up processing time for no reason, and the cues to readers move them towards the intended message, not away from it.
A couple of additional comments:
I'm not sure why old data was cited because in the most recent accounting report, the proportion of government funding was around 65%.
Source of funding is not a useful measure of pro- or anti-government bias, especially in a democracy where different parties lead the government at different times. There are plenty of mouthpiece media that do not apparently receive government funding.