Images: Soil ternary plot, Mike Norton via wikimedia.org, CC BY-SA 3.0. Chip ternary plots, S. Heard.
I’ve always been mystified by ternary plots – you know, those cool looking triangular ones. I shouldn’t be; they aren’t really that complicated. But while Cartesian plots (in two dimensions or three) speak to me easily and clearly, ternary plots remain stubbornly silent.
I’ve survived this cognitive failing for nearly 30 years by deploying a strategy based entirely on avoidance. Ternary plots just aren’t used that much, in my field, except with a couple of specific kinds of data that are conveniently treated as mixes of three components – soil composition (sand, silt, and clay; above) being perhaps the most common. But my avoidance strategy came crashing down around me last semester, when I taught part of second-year Ecology as a sabbatical fill-in. There is was, right there in the 4th week’s lecture outline: soils. Field capacity, available water capacity, wilting point, soil horizons, and – oh, the humanity – that conventional ternary plot of sand, silt, and clay. I had to teach it – and I didn’t understand it.
Something had to give, of course, and I knew it had to be me. Continue reading