I was just building a quick encounter map for the game I have in 38 minutes.. (eep!) and ran across this little hack that people might find handy. I'm using Gabriel Picard's Village to Pillage: Hamlets/Outskirts for a quick rural map, but this will work well for any tile set where the tiles are all the same size and larger than 1x1 unit. Gab's tiles are 20x20 for this set (and many of his sets). I'm making a map that's 3x3 tiles, so while making the map, I set the page size to 60x60 and the grid size to 20 units: Now, when I drag in the tiles, they are stretched to the grid size, which is the exact right size. When done, I just set the grid bac to 1 unit and GAME ON! Hope that's helpful to people!
