Close, The map is set up as a binary search tree. When a particular set of tiles are needed to be rendered, the program will "walk the tree" to get that "section" of tiles.
Here's psudo-example...
Say like we want to get the tile that's in blue, well, we have to transverse the tree, getting smaller and smaller branches in order to access that branch's information. The whole map isn't "visable" in one sitting, You have to "walk the tree" to get the data you want. This is why the FF7 map is in 4 sections (contained in 4 files). Each is a search tree for tiles for each corner of the map. What's cool was the "branches" are interchangable, however the tiles were not. When we tried to alter the "leaves" of the tree, it damaged the search system and caused the map to collapse.
I don't know enough about search trees to hack it, but that's a general rundown of the system.
::EDIT::
But you might say "but the map out of polygons, not tiles"
IN FF7's case, it's made out of tiles, each triange you see above is a polygon. Each "leaf" teminated in little tile model. When we tried to change the model, that's what broke the tree. The FF7 map was 256x256 tiles, this allowed for "repeating" tiles like water, desert and grassland.