Size Matters

…Well, in plan communications and Gantt charts, it does.

Size, when used as an attribute to denote meaning in data visualization, will likely force our brain to look at the largest items first. In her book “Storytelling with Data,” Cole Nussbaumer Knaflic tells us that “Relative size denotes relative importance.”

Size is just one of the preattentive attributes, or visual clues, that tell our brain where to look. When employed correctly, as Knaflic suggests, these attributes can be used, not only to tell our audience where to look first, but also to create a “visual hierarchy” that will allow us to communicate layers of data to our audience in a natural flow. The hierarchy allows us to better tell the story of the data, even in a single visual.

The preattentive attributes in visuals are:


Image credit: Colin Ware, Information Visualization: Perception for Design

Motion was also noted, but not shown above.

Knaflic, smartly, also shows us preattentive attributes in text, which are more obvious, relatable, and make sense to note here, given how often we have text in our Gantt charts:

  • Color
  • Size
  • outline
  • Bold
  • Italics
  • Spatial      Separation
  • Underline

Let’s take a look at a couple applications of using preattentive attributes in a plan communication. For some context, assume that we’re working to communicate a portfolio of potential drug candidates in development. Our executives want to know where the major milestones lie, but the final milestone is the most important.


In the above example, we’ve used several preattentive attribues:
-Enclosure (swimlane border)
-Bold Text

My eyes are first pulled to the large red milestones (then to the legend to figure out what those mean, supported by the other colors/shapes). I then begin to look at the the large bold font within the swimlanes, emphasized by the swimlane borders. The actual bars that connect the milestones are very thin and therefore are not important in and of themselves. This is a hierarchy. With some more work and feedback from others, we could probably get this hierarchical design as close to perfect as we can, but for now, it works.

Here is another example using the same plan, but in this presentation we’ve been asked to point out only the final milestones, as well as anything that is “critical.” Our audience also wants to understand how firm certain estimates are:


Here we’ve used:

-Enclosure (in two ways…swimlane borders, and the blue highlighted box)
-Italicized Text
-Underlined Text
-Bold Text

While the preattentive attributes we used overlap a bit, the two visuals are very different. In this second example, the first 3 milestone shapes in the rows become almost non-existent…they are unimportant due to their color when compared to the final milestone, like the bar/line on which they sit. In this chart we also pick up on a couple of those being black (critical), which makes us drawn to those top two rows much more. Lastly, we now have a light blue box that is highlighting what milestones are considered “directional” with regard to their estimates.

You have probably used preattentive attributes before. But now that you are more conscious of them, we hope that you will reflect on how they might have improved a chart you’ve created in the past, and play with different uses of them in order to make your future visuals even better.

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