I went to create 9 maps for the achievement and I found all my maps (both with and without a compass) were revealing the whole map image when I created them. I thought it would maybe still work when I tried to put them on the wall but it did not trigger.

The problem is I have no idea what parts I still need to explore so it's near impossible for me to fill them out.

I also noticed all my maps had different levels of lighting when I put them in the wall and I don't know if that's an indicator of anything.