Data visualization designer distills essential takeaways from Edward Tufte’s one-day course. medium 
I have absorbed and reformed the ideas into 3 key points, which in my opinion are essential concepts to becoming a better data visualization designer.
1. Visualization design is a research problem.
2. Spatial Adjacency vs. Temporal Stacking.
3. Content is the emphasis
With larger resolution media (paper, tablet), all the necessary information can be adjacent without the need for operational instructions. 100% of the canvas can be used for the content and the audience can have full freedom to explore spatially.
Lower resolution requires temporal stack design. Space limitations divide content into chunks connected through interaction and require "computer administrative debris" for navigation.
YOUTUBE YslQ2625TR4 Tufte critique of iPhone information design is mostly positive
The general theory is "To clarify, add detail. Imagine that. To clarify, add detail."
Clutter and overload are not attributes of information, they are failures of design.
To make better visualization, it’s not about simplifying the data, but clarifying them.
Good design should maximize content reasoning time and minimize time to figure the design and format.
Simple Design + Intense Content
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In college I studied architecture. In my junior year studio class I attempted to produce my final design and present it entirely on computer. The design was fun. The presentation suffered greatly. The contrast between my peers and my own presentation drove home the limits of a computer screen.
My peers had full posters for their final drawings. The detail views of different structural or design elements could float in the edges of the drawing without any comment from the presenter. The images themselves communicated directly to a visually literate audience of judges. The presenters were able to devote their allotted presentation time to only the essential big ideas of their design story.
In my case, I had to spend time showing the details. I couldn't get through the broad story-arc of my design idea.
Now I can summarize that experience as school-of-hard-knocks lessons in spatial adjacency vs temporal stacking.