could you make some diagrams
I hope these do.
Here's a map not broken up into neat squares:
Now when the player is in one of the areas, as soon as those trees show up on the map, it will not scroll the map any further, making an artificial edge within the map, thus confining the camera to that area that the black box shows in this picture:
When the character moves to the next area, say the SW part, the camera pans over to that area, following the player, and will now only look at that area where the black box is shown.