Crossings

Every mapped language sits on the rim, ordered by where it is spoken — grouped into the six macroareas, then west to east inside each. A chord joins two languages in the same branch of the classification tree, and is coloured by family. So position is geography and colour is descent: 2,172 of the 9,259 chords leap from one macroarea to another, and those are the ones that cross the middle.

This is the same set of relationships as the globe, in the other space. There a chord's depth showed how far apart two relatives ended up; here its reach across the circle does. A family that stayed put draws a tight bundle against the rim; one that travelled throws a chord over the centre.

Glottolog 5.3 for classification, coordinates and macroareas. Chords are drawn between languages sharing a branch of at most 40 languages, and only where the two sit at least 8° apart on the globe — closer than that and the chord marks nothing.