What is a line? Cardboard structure 3D>2D,

In the same way I have outlined the simple shapes here, I started to do the same to the pictures I took of the cardboard structure from various angles...

I wanted to flatten the 3D-ness of the structure when outlining with the line tool, much like the process in the publication '3D > 2D'. I was impressed with how much the overall composition of the shape montages varied...