In the book "The Curious Incident of the Dog in the Nighttime," why is Christopher fascinated with illustrations, diagrams, and maps?

In Mark Haddon's novel "The Curious Incident of the Dog in the Nighttime," the protagonist Christopher describes himself as a "mathematician with some behavioral difficulties." It is implied throughout the course of the book that Christopher might have some mild form of Autism, such as Asperger's Syndrome (although I should clarify that this is never directly addressed in the book but is stated in the book's blurbs). 

Christopher's complex mind has many facets and one of those facets is his ability to think logically. This might explain why he is fascinated by illustrations, diagrams, and maps. As a logical thinker, he is naturally gifted at reading, analyzing, and understanding complex images and grids. Being able to study these illustrations takes the stress off his mind. In doing this, his mind feels relaxed.