Concept maps. What exactly they are? I would like you to recommend me a definitive book about concept maps. I've been taking a look to a wide variety but none of them seemed clear to me.
From wikipedia :


  A concept map or conceptual diagram is a diagram that depicts
  suggested relationships between concepts. It is a graphical tool that
  designers, engineers, technical writers, and others use to organize
  and structure knowledge.
  
  A concept map typically represents ideas and information as boxes or
  circles, which it connects with labeled arrows in a downward-branching
  hierarchical structure. The relationship between concepts can be
  articulated in linking phrases such as causes, requires, or
  contributes to. 


The technique was first developed in 1970's by Joseph D. Novak. You can try one of his books e.g. Learning, Creating, and Using Knowledge: Concept Maps as Facilitative Tools in Schools and Corporations