It depends on the solar system and other star/planet factors.
A flat world is really different from a spheric one. Start asking question to yourself: do the inhabitants know something about the world and its flatness? what is at the borders of the earth? is there something on the other side? can one go on the other side?
Well, imo, a flat world could not exist. Maybe a cilyndrical one, with small thickness... anyway it's funny create something weird and unusual like this! Have fun and good luck.
I don't know if these links can help: