System designMediumsd-g144

Subject Proximity searchLevel Mid–Senior~35 minCommon in Distributed systems interviewsIndustries Technology

Question

Design the proximity/presence backend for a location-based AR game (think Pokémon-GO-style) where 10M concurrent players see nearby players, spawned objects, and events within ~500m, refreshed continuously as they walk around. Movement is constant and the world is densely populated in cities. Cover the spatial index, how a client subscribes to its surroundings, and how you bound update volume.

What a strong answer looks like

Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts — data model, bottlenecks, consistency, failure modes — and name the trade-offs you are making.

Learn the concepts

Narrate your design

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Run or narrate your approach, then ask the coach.