Visualization of development indicators by country: (A) Gapminder's original version ; (B), with an additional attribute encoded using D-MO (shown with transparency at the extreme positions of the oscillations) (clik to enlarge).
On a visualization, the position of the marks encoding data is the most expressive and effective visual channel. It conveys order and quantity without impairing the perception of other visual channels. In the field of Information Visualization, position is often restricted to two dimensions, because using the third dimension, depth, usually affects the perception of size, which is also one of the most effective visual channels. We propose a new visual channel, D-MO (Depth from Motion and Occlusion), a combination of visual cues, motion and occlusion, with interactions, that induces a depth perception suitable for combined use with classic visual channels. We characterize the expressiveness and effectiveness of D-MO and show that it is a magnitude channel with good accuracy, acceptable discriminability, and is separable from size. Thus, D-MO opens up new areas for visualization design, which is limited by the scarceness of available visual channels.
A reimplementation of Gapminder's BubbleChart using D3.js shows how D-MO can be used to encode a supplemental quantitative attribute.