Information graphics are meant to carry meaning, so that readers can learn something about data, facts, or processes. But what does it mean to inform? And how does the goal of informing in information graphics differ from analytical visualization?
A key idea in visualization is that of externalized memory or externalized thinking: Using pen and paper to multiply large numbers is easier than doing the same thing entirely in one’s mind because we don’t have to remember all the intermediate results and can thus focus on the actual operations on the numbers. Visualization serves a similar purpose, and goes beyond it by giving us access to amounts of data we could not possibly memorize.
During exploratory and analytical visualization, we query this external representation by looking at it, changing settings, filtering, pointing, etc. What we do not typically need to do is remember any of this, because we can just get it shown to us again very quickly and easily. We have externalized the data storage and so can focus on looking for patterns and trends, coming up with new hypotheses, drawing conclusions, etc.
When it comes to presentation, however, the situation is very different. The point of presentation is to give the person you are presenting to something he or she will remember. There is no point in presenting data or facts if the audience does not take at least some of them away from the presentation. The place we take information with us is our memory.
To inform means to create a memory. That is a different goal from analytical visualization, and thus the techniques and approaches also have to be different. To create a memory, we need to make connections. Our minds don’t store independent pieces of data, but rather connected fragments that we reassemble when we remember something.
Context is critical in this case, as is uniqueness. Using the same style of visualization for lots of different questions and data sets works fine for analytical purposes; it probably even reduces cognitive load from having to switch between irrelevant differences. But for presentation, a chart or visualization that is to convey a particular message has to be different from the ones that carry other messages. Visual presentations are remembered visually, unlike verbal ones (where it makes no difference whether you read or heard something, or in what language).
This is where information graphics succeed and general-purpose visualization currently does not, except as a component of an information graphic. Visualization and memory have not been studied much so far, and given the significant importance of exploration and analysis in visualization, that is understandable. But as we are moving into the presentation realm, we need to pay more attention to higher-level cognitive processes, including memory.