I love the idea that Tufte puts forward at the beginning of this chapter about color as measurement—that something about the intuitive human sensitivity to color allows us to use it as a system of measurement. Rather than dealing in simply color-coded absolutes, like in Burnham’s simple map on pg. 4. Although I’m not consciously aware of the hue, saturation, and value inherent in every color I see, the contrast between two different shades of blue or intensities of the same blue has an immediate, tactile effect. Tufte uses the word “enliven” to describe colors’ effect, and I think that’s as good a word as I can think of: there is a living, dynamic sense to the intuitive understanding of color that can support and enhance more “flat” data.