The background in 'regular backgrounds' is the 'whole' informationen, what can be displayed from the savegame? Is this correct?
This resolution is much lesser, then in 'Mode7 backgrounds'. But there is no other way to get all this background informations?
Mode7 backgrounds are always 128x128 tiles á 8x8 pixels, and games can use only that (Super Mario Kart) or scroll dynamically (F-Zero, Secret of Mana).
BG1 to BG4 use tilemaps that can count 32x32, 64x32, 32x64 or 64x64 tiles, and these tiles can be 8x8 or 16x16 pixels. So one background can be up to 1024x1024 pixels (examples: Yoshi's Island, Ganpuru - Gunman's Proof), but many games use smaller backgrounds and update the tilemap when necessary. In that case you'd have to manually visit every corner of the map, and stitch the screens together.
I tryed to build a world map for Tales of Phantasia (for testings). It has a resolution of 5000 x 5000px. It looks great and its a very easy way.
Great!