Hi, new player of dwarf fortress here, i came across an issue, not really a bug. It puzzled the hell out of me though!
I managed to gen a world with a 5x5 local area that had a very gentle hill with a volcano at the top and a river at the bottom, plenty of sand around the volcano, sedimentary layers near the surface further down, with flux AND iron making ores within 20 Z-levels (no Dfhack reveal, just dug 20 level U/D stairs at the wagon to check). Naturally i saved the seed before i play it (PM me if anyone wants it).
Like i said i'm only a week into the game, (~5 fortresses all the way to 200 pop) but i've already found the goblin sieges unchallenging so i went looking for a mod to improve that before playing the golden embark i found above.
Here's the issue: Installing Difficulty+ changed the land mass generation for the same seed?! I uninstalled the mod to verify this, fixing the land generation but losing the added FUN.
Weird huh, adding civs changes the land mass generation? What it specifically did was turn the temperature of the world upside down, so my desert was now north, and my polar region was in the south. Stranger still, the polar region retained identical shape (albeit rotated 180) even though the land itself became as if using a different seed.
Anyhow, i'm posting in case any other users or the author come across this same issue, it appears race language files are used in the randomisation process for land generation.
Removing the mod languages fixes the world generation to match the seed as generated with a stock game. I did a search for "languages world gen seed" and didn't find any hits so hopefully this is useful for someone.
Big thanks for making the mod by the way! I'm about to go try it out now.