The takeaway from the key brightness map (the central black-and-white band on the sheet of parallel maps above), in terms of how it corresponds with the geographical elements it’s meant to evoke, isn’t as straightforward as with other musical elements that I’ve shared before (like attack and instrumentation). Those other elements show an overall intensification building up to and then down from the musical/geographical “climax” point. But I think what does come across in this one is darker keys corresponding to 1) darker forested landscapes in the middle third of the piece and 2) the ominous mood at the very end as deforested landscapes “appear,” in both the slides and the music, in the distance. (That location in the distance explains the hatched dark-and-light zones at the tail end. Certain voices play in a dark key depicting that distant but encroaching destruction, while the rest play in a brighter key to represent the for-now-preserved foreground.)
Relative Key
I’ve been thinking about key brightness as an “absolute” quality—you can sense how bright or dark a key is even if you hear it in isolation. But with relative key (above/to the right of brightness on the sheet), the relativity is the point—what matters is key changes, or key variability, not characteristics of the individual keys. (For the mathematically-minded among you, taking this a step further would mean drawing a map of the derivative of the key, rather than the keys themselves as I've done above.)
So in this case I’ve represented the different keys as colors along the rainbow spectrum rather than on a greyscale. Similar keys, like C major and G major or C major and A minor, are denoted by similar colors so that the more dramatic the key change, the sharper the color contrast. A greyscale would’ve shown those contrasts too, but each shade of grey by itself would’ve suggested an “absolute,” intrinsic level of something, whether that’s brightness or some other quality. Color indication, however, seems appropriately arbitrary (though, having synesthesia, now that I think about it these colors could in fact represent some absolute quality of each key—maybe a future map?). Plus, key changes are fundamentally changes in musical “color” that outweigh the probably less perceptible changes in brightness. Having said all this though, I’m not totally sure that what I’m perceiving as a “color” change isn’t actually a “brightness” change. Again, I’m not even sure that’s answerable, for my own ears let alone everyone else’s. Think of these as possible ways of experiencing key, whether or not they’re actually distinct.
I wrote key changes into The Last Island to evoke a combination of things: 1) shifts in scenery or atmosphere (overlaid with considerations of brightness as described above), 2) physical exertion/movement of the traveler/listener, and 3) the complexity or “energy” of a particular scene. The zone of rapid key changes around the climax point represents a mix of all three of these. Overall, more and sharper changes in key/color mean a heightening of sensation, which like in the earlier maps tends to correlate with a cumulative intensification of the physical environment. (I don’t claim any originality in using this technique—you’re probably familiar with what’s been disparagingly called the “truck driver’s gear-shift” in pop music, where half- or whole-step key changes are inserted to heighten emotion. I did try to be more subtle than that in most cases.)
Back to the question of representation—using the rainbow gradient, as opposed to another type of color gradient, has some issues. Not all segments of it (say, yellow vs. blue) are of equal “strength” to the eye, and so contrasts between those sections aren’t either. It follows that in the map, the apparent degree of contrast between different keys likely doesn’t quite correspond with reality (if there is a reality to all of this to begin with). So I’ve made a version using a smaller segment of the rainbow spectrum—red to yellow—which doesn’t eliminate the strength disparities but might at least limit the range of contrasts that could be misleading. The two versions are lined up below.