Reverse geocoding service
Design a reverse-geocoding service that turns a raw (lat, lng) into a human-readable address and the administrative hierarchy it falls in (country, state, city, neighborhood, postal code), for 300k requests/second with p99 under 30ms. The reference data is millions of nested boundary polygons plus an address-point dataset, updated occasionally. Cover the lookup, how you make point-in-polygon fast at this QPS, and what you cache.
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.
Clarify4:30 left
Estimate4:30 planned
Design13:30 planned
Deep dive10:30 planned
Failure7:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.