I can testify for anyone who is skeptical that this is the absolute best world map tileset.
I am using it for Crystal Collection and it will be the only set needed. It covers plains, snow, mountains and desert. Plus it layers the ocean so that you get shallows and deeps.
I would HIGHLY recommend this tileset.
As for passablility, only set it as you need it. I guaruntee that unless your making some Uber MMORPG, your not going to use every single tile.
Obviously water and mountains are 'X' but things like buildings and trees you can leave as 'O' because you never know when you will need to walk over something.