Norgutel uses the Mapsforge offline map library. Maps offered for download within the application are from the official high-speed mirror at Rechenzentrum der Hochschule Esslingen, University of Applied Sciences. You can also sideload your own Mapsforge maps (e.g., from your computer via USB) to Norgutel's maps/ directory. Mapsforge themes are supported and expected to be found in Norgutel's theme/ directory. These directories are within Android's standard app specific external (SD card) storage directory. Check out Norgutel's About menu to find these exact paths and other app details that may be specific to your device.
Norgutel supports the GPX format to read and write tracks and POIs (waypoints). GPX files (with tracks, POIs or both) sideloaded on your device from external sources should be placed into the app's tracks/ directory. Norgutel has the concepts of tracks vs. track segments, that is, you may have multiple track segments within a single track. Norgutel also allows a rich set of editing, combining and saving functions, therefore you may create your own track by cherry-picking from other tracks' track segments and potentially adding new ones you author in Norgutel itself.
Norgutel apps use a common server as a rendezvous point so that they can exchange IP packets no matter which network (WiFi, cellular, free or paid) the devices connect to. Norgutel implements end to end encryption and authentication to ensure that all data exchanged within a session is comprehensible only for the participants. (For the tech savvy, you are protected by ECDH/secp256r1, AES-128/CTR/NoPadding, HmacSHA256.) Importantly, the Norgutel server itself is not able to decipher the data either. Additionally, you are encouraged to host your own server to contain all network traffic generated by the applications within your premise (e.g., if you are using the app to track assets on your campus). Note that applications can only exchange information if they join the same session and they connect to the same server simultaneously. Therefore, if you launch your own server, make sure to configure your server's domain name or IP address in everyone else's app with whom you want to join a session. For instructions on getting started with your own server, check Norgutel on Docker Hub for more details.