Geomorphic Tile Key

I've added a feature to each 12"x12" geomorphic tile, an identifying key with directional key.   Each tile has its own I.D. number, e.g.  D2  (dungeon 2), or C3 (Cavern 3).   Below the number is a cross, like a compass rose, only numbered 1,2,3,4 instead of N,E,S,W.   This way, I can prepare a dungeon with the tiles and make up my own secret key ahead of time.    If I write D1--3.   It will mean "tile D1, with side 3 in the "up" or "north" position.