I don't know if it is intented or not, but on my computer I can see some marks in the unexplored areas :http://www.flap.fr/grenier/DD_01.JPG
With a bit of habit it is possible to guess whether there is a wall and its direction.
Also, there often are no walls when reaching the edge of the screen. Is it made on purpose too ?
Finally, it is not a bug but a remark : I guess that a later stage character selection will be done by hovering over buildings rather than pushing these ugly buttons ?
I also prefer selecting character first then the dungeon, as in freeware version. But you are probably planning much more work for the interface ?
The city emerging from the book looks really good.