The idea that Celebrimbor is able to draw a cross-section of the tower of Barad-dûr from memory and feel, as a prisoner, is rather amazing. They're hard to draw even when you have all the information! But then he is the son of Curufin and grandson of Fëanor. 

I love the feeling I get from this that just having the ability to create in some tiny way lessens the cage in which he has been put.  Perhaps insignificant in every way except to his soul.