> Instead of projecting the Earth directly onto a single square, it projects the Earth onto the 6 faces of a cube enclosing the Earth and then applies an extra non-linear transformations to reduce even more the deformations. Each cell in s2 is in fact part of one of six quadtrees that describe the whole planet.
That's a super cool detail! I once implemented a 2D index using a Z-Order curve that directly translated lat/lon coordinates to a linear ordering. It works well enough because nobody really lives at the poles--the search regions with a single projection get really obtuse there. Projecting the earth onto a 6-sided die is a really elegant solution to that problem! Go go Google engineering!
That's a super cool detail! I once implemented a 2D index using a Z-Order curve that directly translated lat/lon coordinates to a linear ordering. It works well enough because nobody really lives at the poles--the search regions with a single projection get really obtuse there. Projecting the earth onto a 6-sided die is a really elegant solution to that problem! Go go Google engineering!