nostrich:

From an essay by Josef Albers, titled One Plus One Equals Three or More: Factual Facts and Actual Facts, written in 1969.

Taken from Edward Tufte’s Envisioning Information, along with this quote:

Visual activation of negative areas of white space in these exhibits illustrates the endlessly contextual and interactive nature of visual elements. This idea is captured in a fundamental principle of information design: 1 + 1 = 3 or more. In the simplest case, when we draw two black lines, a third visual activity results, a bright white path between the lines … Most of the time, that surplus visual activity is non-information, noise, and clutter.