Gps does not use data. It triangulates your location off of satellites. When you use a navigation or gps app it can retrieve your longitude and latitude without data from gps satellites. However once you want to see where you longitude and latitude is located on a map, you must use data to download the map, not your actual location.
So, if you use a gps app with airplane mode on, it will still find your longitude and latitude, however it won't show you the map. If you have a real paper map that's not on your phone, you can find out where you are technically by using the maps longitude and latitude grid.
Some gps apps have a feature to download a map for your gps and it will store it semi-permanently so you don't have to download it again. You usually will have an expiration time to save the map so you can re download it to check for geographical changes or new roads etc. Keep in mind if you are to travel you would be downloading a bunch of map data for the first time as its a new area. Maybe use wifi to route your map the first time at home to download the map data first?