Everything is made of plain filled paths, the character, the background, the graffiti, everything. I first drew a sketch on paper, then put the line-work on top and finally added color and simple flat shading. Does this answer your question?
Good... There's really nothing exciting about the way I work. Most of what I do is click around with the pen-/bezier-tool and later on bend the path segments into the desired shape with the node tool : )