Navigators and sailors used the magnetic compass to determine their heading and maintain a consistent course over open water. By aligning the compass needle with magnetic north, they could accurately plot their position and direction on nautical charts, allowing them to create reliable route maps. This tool was essential for navigation, especially before the advent of modern technology, as it helped sailors avoid hazards and reach their destinations efficiently. The compass also enabled them to account for magnetic declination, ensuring more precise navigation across varying geographic locations.