If you place your image inside a box so that the glowforge engraves the map and then cuts the box you are left with three issues I can think of:
- The laser cuts down the center of the box, so there should be a white space border between your image and the box equal to half the width of the kerf at the surface of the material.
- Unlike a perfectly balanced saw blade, the laser doesn’t leave you with a perfectly vertical edge. It should be slightly wider at the top than the middle, where the two pieces of wood will first meet when they butt up against each other. This is pretty slight on 1/8" material, but it will leave a line.
- The cut operation doesn’t adjust power for corners, so there is a tiny amount of overburn at each corner. The only way around this I know of is to use the engrave operation to cut-through the material instead of the cut operation. This increases the time to make a tile, but these aren’t exactly going to be quick.
My suggestion is to take a small section of one of the tiles, place it inside a box and do some experiments with the material you are going to use. Once you have your kerf and engrave-cut versus cut decisions made, do one full size tile. It is possible the kerf doesn’t scale perfectly and it seems you are aiming for perfect.
If your plan is to pre-cut the wood and then place the image over it, well the accuracy will be better than 15th century printing technology. You can make a jig and if each of your twelve images are placed at the exact same coordinates on a 12x20-inch art board it will be accurate, but not as accurate as the first method because of the tolerances in the pre-cut wood and its fit in the jig.
No matter how you approach the tiles, I would recommend finding a helpful glowforge owner when you’re done with your first tile. The point being to see if the cloud software will successfully process your file (not to have someone actually print it.) While the software is continually improving, a particularly large file may just not print at this time. Sadly, you can’t tell just from file size - you have to try and see what happens. If this would turn out to be the case you would either need to make a map with more, smaller, tiles or wait for the software to catch up.