Would it work to fill the entire land with "dirt" first and then just cover it with other terrain types without using any special rules? You might end up with some dirt between other types of terrain but this is what HOMM I and II we doing too. And I'd guess they did if for similar reasons.
Also - how far did you go with auto-tiling? Can the effects of your work be seen somewhere?
So I think you're talking about giving each biome a layer and stacking them on top of each other. That works for 98% of scenarios. But any time you have a section of width/height 1 tile, you run the risk of covering it up by another layer. (at least in a 2x2 bitmask, may not be an issue in a 3x3. ) I did that for the longest time, until I started noticing small peninsula's and bays in my ocean were appearing/disappearing where my code said there wasn't one. Place a single random tile of iceland in the dirtland and depending on how you layer things, it can vanish entirely.
I have my auto tiling working pretty damn well at the moment. lacks a buttload of polish, but it even wraps around. The ultimate goal I'm trying to do is be able to "lock" tiles into place and then reroll the world around them. I haven't actually tried exporting something in godot yet but I bet I could throw something up in github once I figure it out.
If people are interested
