Puzzle 275: Tetra Firma 18

275! It's a number! It's a big number! And it's the number of this puzzle, which is a big puzzle!

Normally, when I decide I want to post a huge 31x45 puzzle on my blog to celebrate some milestone like 275, I have the puzzle made many days, if not weeks, in advance of actually reaching that number of puzzles. However, in this instance, I didn't even decide I would have a giant puzzle for 275 until last night. The initial construction was done in about three and a quarter hours; it took about half an hour more to create the image, after which I went to bed. Vetting the puzzle and fixing a mistake I found took about three hours. My brain is now kind of throbbing from all of those hours -- I hope you're happy!

By the way, if you happen to find some regions in the grid that are shaped like digits, such as, say, I dunno, 2, 7, and 5. . . that's just a total coincidence.

Rules of Tetra Firma
(click to enlarge)