I managed to wrap up the extra code in the world building editor interface to handle applying (and removing) spawn locations, resource locations, and applying the correct realm to each tile location. It will nicely show me the overlay in a simple colour coded effect, so I don't need to worry about setting anything once I've picked the right realm to apply - and spawns & resources was even simpler.
Here I've applied one realm to the waterline at the top and one to the land to the south of the river - which means that I can now control spawn items exactly how I want them, same for creatures and all the associated bits of pieces.
I really thought this would take longer to get done, but I am totally not going to look this gift horse in the mouth, but rather start on the next bit of work - which will be in the app again, working on creature logic to work towards starting an encounter. I think all the other ducks are lined up nicely, so hopefully a little bit there, and then I get to start on what combat looks like finally.