Turn-by-turn navigation is a feature of some satellite navigation devices where directions for a selected route are continually presented to the user in the form of spoken or visual instructions. The system keeps the user up-to-date about the best route to the destination, and is often updated according to changing factors such as traffic and road conditions. Turn-by-turn systems typically use an electronic voice to inform the user whether to turn left or right, the street name, and the distance to the next turn.
Mathematically, turn by turn navigation is based on the shortest path problem within graph theory, which examines how to identify the path that best meets some criteria (shortest, cheapest, fastest, etc.) between two points in a large network.
