How wide a margin each band reads a plate property over.
They are the support radii of plateProperty's weights: a plate this much
farther from the sample than the nearest one has no say in that band. They
genuinely differ, which is why there are three rather than one — hypsometry
changes crust type over a shelf and slope, a mountain belt is an orogen wide,
and an arc's volcanoes sit closer to the trench than either.
HYPSOMETRY_MARGIN is a quarter of a radian, ~1,600 km on Earth: a
continental shelf and slope together, and the scale over which the crust
actually changes type. BELT_MARGIN is a tenth, ~640 km, which is the width
of an orogen — the Andes are 700 km across including the foreland.
ARC_MARGIN is 0.06, which is where the volcanoes are rather than where the
orogen is.
None of them may exceed PLATE_MARGIN, which is how far plateAt
bothers to look: a band blending over a wider margin than the search would be
dividing by a sum it had already truncated, and the answer would jump as a
plate fell out of a set it still had weight in. geology.test.ts holds the
three against it.