My suggestion:
GPS Panel uses GPS only if a GPS is present, otherwise it defaults to a config file that, at this point, could be unique for both GPS and Astro panels.
If no config file, then the weather app, as you already do, could be second choice.
This way you simplify it a bit.

In StellarMate, all system's coordinates are got from the mobile app: sometimes, even if I use StellarMate at home, I first connect to it with the mobile app, just to set or update the gps position.
Is AstroBerry we do non have a mobile app (yet...) so a unique config file could be the solution.