What Tufte seems to be getting at with layering and separation is that the space between objects by their creation, and the space taken up by the objects created has a heavy impact on information graphics. Using bold, thick lines, clunks things up by leaving less separation and makes things harder to scan through effectively. The concept that Tufte kept coming back to was Albers' "1+1= 3" concept. This concept explained that "one line plus one line results in many meanings" and that it's all about how the images are arranged that brings out the meaning within them (pg. 61).