Proximity / Geo Search

Finding all drivers within 5 km of a rider sounds simple, but a standard database index can't answer it efficiently. SQL B-trees are one-dimensional — they can't bound a circle. Geohash encodes latitude/longitude into a short string where shared prefixes mean physical proximity, turning a 2D range search into a fast prefix lookup. Redis GEOADD/GEORADIUS implements this internally, handling 200K location writes per second from 1M drivers with sub-10ms query latency.

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