GPS can work without data - since primary GPS uses satellites to triangulate your location, that can be done without cellular or wi-fi data. That said, accuracy is typically better when it can use cellular towers and local known wi-fi access points to more precisely locate you (or do it more quickly) - and I'm honestly not sure whether that aspect of it uses data or not. However, the main source of data usage with GPS is downloading the map data. Many apps (including Google Maps, OSMAnd, and HERE Maps) offer the option to download maps to your device. This reduces data usage, and can also allow for completely offline or data-disabled usage if desired. I've used all of those in an airplane (while on airplane mode, manually turning back on location services) and I'll at least occasionally be able to get my location - depending on how close I am to a window, whether that window is facing generally south, etc.