To find drivers near a rider, you look up the rider's geohash cell. Why must you also search the neighbouring cells?

Options

• ✗ Geohashes are only accurate in the northern hemisphere
• ✓ A driver a few metres away can be just across a cell boundary, with a different prefix Correct
• ✗ Each cell holds at most one driver
• ✗ Neighbouring cells hold the drivers' history

Why

Cells are a grid, and a rider near an edge is closer to the next cell's drivers than to the far side of their own. Querying the cell and its 8 neighbours covers the area around them.

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