As The Crow Flies

Walk 300 meters north, turn, and walk 400 meters east. How far are you from where you started?

Not 700. Your path made a right angle, so the straight-line distance back is the hypotenuse: √(300² + 400²) = √250000 = 500 meters. This is how map apps turn your grid of streets into a direct distance, and how a pilot finds the shortest line between two points.