What you do is use the SHIFT commands which scroll the matrix textures, normals and heights. So as you cross a tile boundary, you shift the matrix, move the matrix and fill the edge textures, heights and normals from an array.
If you look on my website, you will find my alienware compo game which does exactly that. I've even posted the source code.
Game uses a 300 * 300 array but the matrix is only 79 * 79. So with some simple maths you can wander around the matrix and shift, move and populate it as you go. The advantage with this method is that game land can be as big as you want.
The game also has the level editor builtin so you can swap between play mode and edit mode at will. No documentation though but lots of rem commands should explain things well enough.
Boo!