A couple a weeks ago, I attended the conference An Event Apart in Boston, MA.
There I heard a presentation by Jason Santa Maria who talked about the narration of design. He briefly touched upon the french engineer Charles Joseph Minard and his Carte Figurative (from 1861) showing the progression of Napoleon and his army to Moscow and back in the
campaign of 1812.

The chart is famous for it's clear and simple communication of something incredibly complex, difficultly graspable and horrific (i.e. the progressively lower number of soldiers in Napoleon's army in relation to temperature and location).
Thereby the chart has become quite a guiding light for designers everywhere trying to communicate complexity with simple measures.
Another presenter at the conference Jeffrey Veen also referred to Minard's Carte Figurative. He pointed to the fact, that Minard himself said this beautiful thing about the chart:
"The aim of my carte figurative is ... to convey promptly to the eye the relation not given quickly by numbers requiring mental calculation."
Veen - a former designer at Google Analytics - has this insight to offer:
"Well designed sites "convey promptly to the eye" what's possible, while doing so
intuitively as to avoid "requiring mental calculation." That's not to say we
should treat people as stupid. Rather, we should help them focus on what they're
trying to do, rather than struggle with the means for achieving it."