Book: System Design Pocket Guide: Interviews — 15 Real System Designs, Step by Step My project: Hermes IDE | GitHub — an IDE for developers who ship with Claude Code and other AI coding tools Me: xgabriel.com | GitHub A driver in San Francisco taps "online." Their phone starts emitting GPS updates every few seconds. As a back-of-envelope estimate: a few hundred thousand active drivers on a Saturday night, one update every ~4 seconds, lands you on the order of a hundred thousand location updates per second. The proximity query a rider triggers when they tap the request button needs to come back well inside a sub-200ms latency budget. This is the part of the Uber design question interviewers actually care about, and the part candidates rush past on the way to "we use Kafka." The interesting work is the proximity index. Given a rider at a lat/lng, return the 20 nearest available drivers in a low-millisecond query, while the underlying data is overwritten many times per minute.…