This document discusses using graphs and breadth-first search (BFS) to model flight routes and implement GPS navigation. It provides examples of: 1) Representing flight paths between cities as a graph with cities as nodes and flights as edges between nodes. 2) Using BFS to find the shortest route between two locations by visiting neighboring nodes first before moving farther out. 3) How BFS works for GPS by treating roads as a graph and finding the closest path between start and end points without allowing diagonal moves.