Real-time location matching

Design the real-time location-tracking and matching system for a ride-hailing / delivery platform. 2M drivers send GPS pings every 4 seconds; riders request a ride and must be matched to a nearby available driver within ~1 second; riders also watch their matched driver's marker move live on a map. The 'find nearest available drivers' query runs constantly and must be fast over a moving 2M-point set. How do you index moving locations, run proximity matching at scale, and stream the live driver position to the rider?