For A9 (not sure which other models), the GPS works by connect to the smartphone. But is this supposed to be automatic? Or do I have to launch the app each time I want to establish the link? Because so far with my a9, it doesn't do it automatically with my iphone.
The simplest approach is to use a GPS logger, and time-sync your phone and camera before you go out.
The simplest way is the way Sony used to do it - with GPS built into A-mount and Cyber-shot cameras. No E-mount camera ever had that; and once that omission established a precedent, Sony began stripping GPS out of
all cameras.
The next simplest way is the way the A99II and, more recently, the A9 do it - with GPS provided by a Sony app running on a smartphone paired to the camera via Bluetooth.
Both of those ways embed GPS data into the files as they're shot, while they're still in the camera, and the job is done.
The most complicated way is a separate GPS logger that requires manual time syncing and after-the-fact transfer and embedding of GPS data into the files using a computer.