Why visualize graphs?

Example: book topic relationships 
[Godel, Escher, Bach. Hofstadter 1979] 

Turing - Halting problem
Halting problem - Infinity 
Infinity - Paradoxes
Paradoxes - Lewis Carroll
Infinity - Lewis Carroll
Infinity - Unpredictably long searches
Infinity - Recursion
Infinity - Zeno
Infinity - Paradoxes
Lewis Carroll - Zeno
Lewis Carroll - Wordplay
Halting problem - Decision procedures
BlooP and FlooP - AI

Halting problem - Unpredictably long 
  searches
BlooP and FlooP - Unpredictably long 
  searches
BlooP and FlooP - Recursion
Tarski - Truth vs. provability
Tarski - Epimenides
Tarski - Undecidability
Paradoxes - Self-ref
Epimenides - Tarski
Epimenides - Paradoxes
Epimenides - Self-ref
[...]

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