Humans have evolved to command immediate attention to moving objects.

Motion is the most powerful retinal variable for encoding information. Its effect trumps that of all other retinal variables.

In accord to the Gestalt principle of common fate, motion is also useful for classify moving objects into common groups according to the direction and speed of movement. That is to say, objects that move together in a certain direction are perceived as belonging in the same group (they have similar characteristics), by comparison to objects moving to a different direction or objects that remain stationary.

When working with motion, it is important to be economical in all other encoding choices otherwise we be overwhelmed with information. If other encoding choices are still important then one could temporarily suspend their visual prominence while motion is at play and then reveal the rest of the information in the final frame when motion stops.

GIF flip book animation

Motion is applied in the same way as a flip-book animation:

The key to working with flip-books is to hold all encoding choices and graph dimensions constant, and only vary the data that is encoded using motion.

Then we must generate a series of images, save them in PNG or JPEG format, and then overlay them using a GIF generator (for Graphics Interchange Format) that would give the impression of movement. There are several free online GIF generators, e.g. Giphy, Gifmaker. As an example, see the analysis on Tribute to Hans Rosling.

GIF movie animation

Alternative to GIF, one could could use iMovie in Mac OSX or MovieMaker in MS Windows, or some other similar software, to create a movie from the images.

GIF has the advantage of low storage size but the generated animation is fixed. Movies have much higher storage size but we can control the animation using pause and resume, rewind and fast forward.

The process is very easy. As an example, consider the analysis on Tribute to Hans Rosling. In that discussion, I present a screenshot from iMovie on how the movie project would look like. Here is that screenshot again:

All you need to do is simply drag and drop all graphs saved in PNG or JPEG on a new iMovie project. Then, select all files (Cmd+A) and click on Cropping in the top right hand side menu, and choose ‘Fit’. Then, click on the information icon (shown as ‘i’ in a circle) and a ‘Duration’ box will appear, as shown in the top right of this screenshot. There, you can adjust the duration of each transition from graph to graph. Finally, go to File > Share > File… to save the project as a movie.

Small multiples

Small multiples, also known as a ‘trellis chart’, is a data graph technique that collects many charts that respect the same encoding choices except one, and then lays the many graphs side by side in a matrix of columns and rows. The data graphs can be of any form.

A flip-book approach is a similar concept to small multiples, but instead of laying the graphs side by side, we overlay them in a flip-book.

Therefore, if the graph is intended for publication in an outlet that does not support GIF animation or movies then the next best alternative is printing a small multiples graph.

Here is. an example of a trellis plot for the Australian age distribution over time:

This is a small multiples collection of 47 graphs and a legend, placed side by side. I like to think of small multiples as a pseudo-animation graph, because the main utility of the technique is to use ‘move’ our eyes from one to the next graph.

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Demetris Christodoulou