Originally Posted by
Ryllharu
From what I've gathered, humans live in the southern hemisphere entirely. Demons live in the demon realm, which is connected to the southernmost regions of the human realms by the huge teleportation gate of standing stones.
Until Maou appeared, humans seemed entirely dependent on wheat alone. Southern nations are poor and live in snowy, cold climates. Too cold for wheat, but ideal for potatoes and other hearty plants. Rye would probably work well too. The further north you go, it gets hotter. Maou mentioned that the corn needs to get to at least 30C (86F) to bud, so they seem to be concentrated in an area where the climate resembles northern Europe and southern Scandinavia, flipped into the southern hemisphere. The northern, more arid and hotter regions are wilderness, unsettled. The central areas are temperate and perfect for wheat.
Then the demon realms are depicted even further south on the maps, but their climate is far more arid in general. The demons entered through the gate and claimed one of the southernmost islands, snowy a large amount of the time. Yuusha said he could end the war by destroying that gate. That combination leads me to conclude the demons live in a separate world connected to the human one.