Remember a couple weeks (months?) ago when google changed their maps from being a flat Cartesian style to having a more polar spherical look to them as you actually moved away from the surface of the earth? This is the library responsible for that.
As far as I know, the map tiles google serves are still in mercator projection -- it's just that mercator was always designed to be projected onto a sphere, not a plane, so now it looks better.
What S2 is, is a better way of representing sets of coordinates within GIS systems, such that searching for features that are close to each other, or within a complex polygon, can be performed much quicker than with other coordinate reference systems ie. floating point latitude/longitude pairs. They're storing points on a 3D sphere (unit vectors) as easily subdivisible 64-bit integers which have a logical order which is much faster to index / iterate over nearby areas.
Makes sense for applications like google maps; "find local businesses near point X,Y" etc.
If I remember correctly, he also mentioned something about the same project being responsible for better stitching and less overlaps/voids in the map.
Thanks for explaining though, helped me understand things a bit better.
Honestly, it's one of the best abstractions I've ever used.
Also, I'm not a mathematician and everything I know about computer science (and most of math for that matter) I've taught myself or learned on the job. So... maybe I'm using the wrong terminology?
I'm 98% certain the library is the same one currently used on google maps web app.