<p>I'm 100% sure that the Human and Spirit worlds are completely different things. Maybey the World of Humans is the same size as our Earth, but only a fraction of it is covered by land.
</p><p>The rest may be covered by a large ocean. I even doubt that there are other, smaller islands in that ocean, only water. If there were other smaller islands, the Avatar could have been born on one of these islands, and the world would be plunged into chaos.
</p><p>And here's a more personal note: The Legend of Korra made everything so much more complicated (and not in a good way). When we had ATLA we knew that there were two worlds, one for humans and one for spirits, and that the most imporant thing to do was to keep balance. We didn't care about modern physics and planetoid movements, we were more engulfed in the spiritual idea of the two worlds. TLOK made EVERYTHING worse. It introduced us with modern technology (so stupid), it completely destroyed bending (seriously, after watching pro-bending, I HATE bending), and the technology made bending useless (why do you need benders if you have modern machinery).
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