s2-geometry-spatial-indexing
S2 Geometry Style Guide
Overview
S2 is Google's library for spherical geometry and spatial indexing, used internally for Google Maps, Google Earth, and countless geo-aware services. It solves the fundamental problem: how do you efficiently index and query locations on a sphere?
The library was developed at Google and open-sourced in 2017. It powers proximity search, geofencing, spatial joins, and geographic sharding at planetary scale.
Core Philosophy
"The Earth is not flat. Your spatial index shouldn't pretend it is."
"A good spatial index turns geometric queries into range queries on integers."
"Locality in space should mean locality in your index."
S2's insight: project the sphere onto a cube, fill each face with a space-filling Hilbert curve, and encode positions as 64-bit integers. Nearby points get nearby integers. Geometric queries become range scans.