The December solstice occurs between the 20th and 22nd in December, which is when the Sun reaches its most southerly excursion. Around this time, the northern hemisphere experiences winter, and conversely, the southern hemisphere experiences summer.
If we try to plot the areas that are having daytime and nighttime on the so-called ‘flat-Earth map,’ the Sun would appear to illuminate an impossible area, similar to Batman’s bat-signal. This fact tells us that the ‘flat-Earth map’ does not conform to reality.