shadow has the best idea. My alienware compo game does exactly that. As you cross matrix tiles, you shift the matrix and update the tiles, heights and normals of the edge from a huge array.
If you look on my website, you can download the game and the source code to see how it all works. Matrix is 79*79 tiles but the landscape is 300*300 tiles but could easily be 10000*10000 if you wanted, with no slowdown. Would take you a long time to walk from one side to the other but at least it is possible. The hardest thing is actually filling and texturing such a huge landscape. My game has a built in matrix editor.
Boo!