Notes on comparing the Avatar world map to our own planet, using AlisaChristopher’s excellent fan-map:
If you assume that the Atla-world is about the size and shape of Earth, then the first thing you notice is that there is a lot of unmapped space. The Avatar map covers ~215 degrees of longitude, leaving ~145 degrees unaccounted for. In comparison, this is greater than the area covered by all of North America, from Labrador to Alaska. Is this area all ocean? I’d assume so, but who knows…?
The Fire Nation looks about equivalent in area to the continental US, though more spread out.
Both the Northern and Southern Water tribes are about the size of Greenland.
If we assume it’s to scale, Ba Sing Se is larger than most countries. The outer wall covers an area a bit bigger than Saudi Arabia, and the inner wall (the city proper) is about the size of FRANCE.
The lakes near the Serpent’s Pass together are equivalent to the Mediterranean basin.
Chameleon Bay is about the size of the Arabian Sea (the area between the Arabian Peninsula and India).
The Equator passes through the ‘eyes’ of the Fire Nation, straight through the Si Wong desert, and by the mouth of Chameleon Bay.
The tropic of Capricorn passes through Chin Village and Gaoling in the south, and the tropic of Cancer goes right through the Serpent’s pass. All of the Fire Nation lies between the two tropics. The Earth Kingdom lies between ~35 degrees south (think Tasmania) and ~60 degrees North (think British Columbia).
In terms of latitude, the Fire Nation capital is right north of the Equator. Think Indonesia.
Haru’s Village is at the same latitude.
The Cave of Two Lovers, Omashu, and the Library are all on a latitude just south of the Equator. Lima, Peru is comparable.
Atmospheric circulation and climate are likely different in the Avatar world than on present day Earth, since the climates we see in the show and the latitudes where they appear are not consistent. For example, the center of the Earth Kingdom, where the Si Wong Desert is found, should be as lush as central Africa or Brazil, with plenty of rain. There may be a rainshadow effect, but this would be unlikely to create such a large and dry desert as we see in the show. Other examples include Jet’s forest, which ‘should’ be a desert, and the Southern Air Temple islands, which should be lush like New Zealand.
The two Water Tribes are not entirely within the Arctic circle, as defined on earth. Their equator-ward parts may melt in summer.
With these findings, it seems that the Avatar World is colder and drier than our own, with widespread deserts and latitudes that stay frozen when they would be seasonally melting, under a climate like our own.
Of course, there could also be spirit magic. Who knows.