I think the layering part of the chapter is very well represented by the chart on p. 55 with the different color separating the different train routes. I also like the map on a later page as an example because it brought to mind the map books that I used to see in my parents' car before GPS devices and smart phones made navigation almost effortless. I think the author was trying to bring attention to the fact that information designers consciously decide to make certain things about maps, charts, graphs, infographics, etc. clear by using certain elements, colors, lines, and symbols to visually separate different aspects of that information. A simple indentation, line, color change, or page break can make a document more valuable.
"To direct attention toward the information at hand, the revision below extends the light to dark range of color, separating and layering the data in rough proportion to their relevance..." p. 63
I picked this quote from the chapter because I like that whole page and the difference between the two graphics. I noticed the bottom image is on the cover to represent the chapter, and it shows the relevance of the topic and how different layering and separation using colors and lines etc. to separate each of the images can add value to a document.