Google Maps is unreasonably fast. Let me explain

Mapping apps achieve instant routing by using a hierarchy of roads and pre-calculated shortcuts, which allows them to ignore unnecessary turns and focus only on the most efficient paths across a network of millions of intersections.

• Computational limits — Calculating every possible route on a continental map would involve trillions of combinations and take centuries to solve by brute force [00:19].

• Dijkstra’s Algorithm — This foundation method searches for the optimal path by radiating outward in all directions equally, which is mathematically sound but too slow for large-scale navigation [07:46].

• Directional guidance — The A-Star algorithm improves upon basic searches by adding a heuristic that prioritizes nodes closer to the destination, effectively pointing the process toward the goal [11:49].

• Customizable Contraction Hierarchies — Modern systems organize the road network into a hierarchy of importance, allowing the software to jump between major highways rather than checking every local street [18:42].

• Three-phase process — To maintain speed while keeping data current, the system splits work into distinct stages:

  • Node ranking — Identifying critical intersections and bridges to create shortcuts that bypass lower-level roads [21:06].
  • Traffic updates — Recalculating the costs of those shortcuts when road conditions or closures change [25:52].
  • Rapid querying — Executing the final search, which relies on the pre-made shortcuts to return results in mere microseconds [26:24].

• How does A-Star prioritize movement toward a target?

• Why does adding shortcuts to a map prevent the algorithm from missing the shortest path?