Startup Idea : Textbook Navigation

I have a vision that text books should use a google map style to present content. Because when I am reading something new in a branch of knowledge I am not familiar with I always find myself lost (where am I?) in the middle of the book forgetting where what I am reading right now belongs in the overall context. Maybe this is just how my brain works but I think that is common. So I would love to mouse wheel to zoom out and check where exactly I am. So the street view would be like opening the pdf file itself and read it normally. Instead of page up and down (like in a normal book) we should navigate like in a map (with several levels like street, neighborhood, cities, states, country etc). Each area size would correspond to the sun of pages of all pdf files inside that area. Of course we can think of features like marking places you have already visited, pre-requirements to understand some text could be seen as visa and so on. The author of a book instead of making a simple table of contents would make a map (in fact any reader would be able to make his interpretation of the book and create a map other user could use). I can detail.