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It's hard to appreciate due to how truncated everything is in-game, but if it can be assumed that Paldea is the same size as the Iberian Peninsula (and there's no reason to assume it isn't the same size if not even larger), then the Great Crater of Paldea has a rough diameter of about 90-100 miles, depending on where you draw the line. Wider still if you include the mountains surrounding it (for the sake of this exercise, I won't).
To put that in perspective, the chunk of New Jersey and New York making up the Unova Region has a diameter of about 30 miles in the real world. You can fit the entirety of Alola's Ula'Ula Island (the Big Island of Hawaii) inside the Crater with room to spare, or toss the other three main islands and a free Unova. You can fit the entirety of the Kanto Region inside it.
All of Area Zero is the Great Crater, but not all of the Great Crater is Area Zero. To reach Area Zero on foot, expeditionary teams needed to hike through unknowable dozens of miles of extremely hostile flora, fauna, and geography just to attempt to breach the epicenter. The walking graveyards that make up the Greavard and Houndstone population are a testament to just how successful those efforts were. It makes the glyphs within the Area Zero cavern all the more poignant--whoever carved them never made it out, but managed to prove that they made it farther than anyone else.
In the span of ten years, the Professor's meme machine released enough Paradox Mons to put the entire ecosystem of the Crater on the brink of collapse. If we can trust by its name that Area Zero is the absolute center of the Crater, that is a hunting range three times larger than the largest territory range of a Grey Wolf pack, six times larger than the American Bald Eagle, ten times larger than the roaming range of a male Grizzly Bear, and forty-two times larger than an African Lion pride.
In conclusion, Paradox Mons are fucking nuts.