Map matching
Design a map-matching service that snaps noisy raw GPS trajectories onto a road network at scale — 100k trips/second of replay plus real-time streams — so that downstream traffic estimation and trip pricing use clean road-aligned paths. GPS is noisy (5–50m error), sparse in tunnels, and ambiguous at parallel roads/overpasses. Cover the algorithm, the road-graph access pattern, and the latency/accuracy trade-off.
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.
Clarify5:30 left
Estimate5:30 planned
Design16:30 planned
Deep dive13:30 planned
Failure9:00 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.