[mrkgnao]

Quick note that may be of interest: S² is the mathematical notation for the "2-sphere", aka what we call a sphere in everyday language. I suppose that's explained by this:

> A unique feature of the S2 library is that unlike traditional geographic information systems, which represent data as flat two-dimensional projections (similar to an atlas), the S2 library represents all data on a three-dimensional sphere (similar to a globe).

(S^2 if the superscript character doesn't show up for you.)