Although you may have started using the word "externalize", and I can see why (and am hard pressed for a better word), and DA may or may not have picked it up from you, I think that it is not a great choice. In the mental health field the word "externalize" is used to describe a process of blaming and attributing actions and outcomes to factors outside of the actor's own motivations or behavior. When the process of externalizing is used too often to explain one's own behavior, it suggests that one is defensive, avoidant of responsibility in that area, ignorant of more complex reasons for behavior, and so on. So, the word may have negative connotations to some people. In regard to GTD processes, I feel that it is less confusing and more useful to use words like "chart", "model", "visually represent", tangible representation", "sketch", etc..