Flipping the script here...
I had an idea for a group of cultists who believe their world is round, even though their world is actually flat. And that got me thinking...
What mechanical changes would need to happen, if any, to make a flat world different from a round one? What mechanics could you play around with? Obviously gravity comes to mind, and you'd have to have some reason things 'fall down'.
This is more stream of consciousness than anything else, but I'll check back in when I ruminate some more.
Depending on how close the sun is, and how close to the edge people live, you could see very different seasons and climate patterns to RL. Terry Pratchett thought about this a bit, and he's not wrong that the center of the disk would be the coldest part - the sun would never get as close as it does further out. I haven't read it but his book The Science of Diskworld is probably relevant to you.
How 'flat' is 'flat'? What I mean is, is it flat in the sense of the Discworld or is it flat with 'warp' edges? In the latter case it would be harder to prove its flatness since, effectively, the edges meet one another more or less like they would on a round world.
The biggest issue would be shadows since on a flat world shadows would all be of equal length regardless of how far apart they are. Though, if it's like the Disc then light would be slower than sound so could allow for different time zones and such.
In the Greyhawk setting, the sun and all the planets orbit around Greyhawk. What do you supposed that does to the other planets’ seasons? :D
I had an idea for a group of cultists who believe their world is round, even though their world is actually flat. And that got me thinking...
I would probably have it be slightly dome-ish. The horizon becomes very difficult to describe/understand. Like being at the top of a mountain, you would be able to see for a very very long distance even if you were like 50ft off the ground.