geo proximity

A rider taps request and within seconds a nearby driver gets assigned. The interesting problems are geospatial indexing of moving drivers, the matching objective (nearest is not always best), and handling the race where two riders want the same car. Here is how to build it.

Find the 20 nearest restaurants within 5km, fast, for millions of users. A naive distance scan over every place is hopeless. The design centers on spatial indexing, geohash or quadtree partitioning, and coping with dense cities versus empty regions. Here is how proximity search works.