All GPS signals are free satilites and no cellular service required, you just need a GPS receiver. Your DJI has built in GPS that locks in during boot up.
Early iPhone & iPads required cellular / wireless to locate GPS... thst’s why iPhones weren’t any good outside in country with out cellular. That changed with iPhone 6 series.
Apple included GPS in the Cellular + Wireless model and did not include GPS in the Wireless model. You don’t need cellular service activated on an iPad to use GPS.
You can turn off cellular, wireless & Bluetooth and GPS will locate like any GPS. NOTE... if you don’t have maps preloaded for your area, it won’t show maps, just a location dot. Regular GPS has full pre-loaded maps... such as Garmin systems. Bicycle computers often have GPS to map & record the ride data,
I use an iPad mini cellular with no cellular service for Inspire RC, download all the maps for google, and/or grab an navigation app that preloads the maps. Use a Android Phone never activated for my Mavic screen, all Androids have built in GPS too.