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System design interview question

Design a heat map for Uber drivers

Medium · System design (HLD) · Company tags: Uber

The prompt

"Design the surge heat map that Uber shows drivers — a coloured overlay on the map showing where demand is high right now, so drivers know where to go. It updates every couple of minutes across every city you operate in."

What this round really tests

real-time spatial aggregation — turning a firehose of individual events into a small, coarse, cacheable summary. The best insight available is that the output is shared by all drivers in a city, making it enormously cacheable, and that coarse resolution is a feature because it both reduces cost and avoids exposing individual riders.

Clarifying questions worth asking

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