HELP ME!!!
So you want the map to scroll in chunks of single-screen areas? What exactly is your problem?
That's what I want. I almost got it working, but it's a little too complicated, and I feel like I'm using g too many variables. Message me if you need some more clarification. Also the game is titled "WORLD(HELP ME!!!)". I'll be more than happy to put you in the credits and maybe even an Easter egg if you can help me out. Also, if you want, I can code a song for you in return.
I'm not entirely sure how your code is working, but I can give you a basic premise of how this goes down:
You already seem to have grid movement down, which is good. (If you want to make use of the circle pad for orthogonal movement, I left an example of that here).
What you may want to do is have an MX/MY variable to tell the game which screen you're on. When you move far enough to the right, the player is set the the leftmost position of the next screen on the same Y axis. Same for going down, left and up.
Another thing you'll want to do to avoid bugging into border walls is having the "inverse" wall on the other side of a transition area. (Say, if you have a tree in the rightmost position on Y point 5, have a tree on the screen to the right in the leftmost position on Y point 5.)
Sorry if you knew this or if it didn't help; this is the info I can give.