I want to do something, so I’m going to figure out how to do it by describing all the ways it can’t be done.
I want to build a flat world for a fantasy novel.
The characters would be able to see mountains from an awfully long distance away. Communications between nations would be an issue of mirrors and weather. In general air a little higher has less particulate matter than air a little lower, we’re talking distances of a few hundred feet, so people would build giant towers to talk to each other when there’s a little fog or high winds. It doesn’t make all the difference, but it would make some, especially for communications across thousands of miles.
There’s the isue of the Sun. Suppose the fantasy sun rises in the east and sets in the west. Doing basic trig, they could figure out how far away the sun is, and from that the direction of the gravity vector. So what? Well, you couldn’t have coriolis force weather patterns, so no hurricanes/cyclones or tornados. Lands to the far north and south, orthogonal to the ecliptic, would get much less light. That’s fine.