The geometry of a globe and a flat plane are quite different. If we live on a globe we expect to find two symmetrical halves, one in the north and the other in the south. If the earth is a flat plane with the north pole in the center and Antarctica as a ring around the circumference and the equator a circle dividing the central and outer portions then the central portion [northern hemisphere] would be quite different to the outer portion [southern hemisphere].
So flat earthers attempt to show distances in the south covering the same degree of latitude as comparable latitudes in the north are greater.
Any hint that the earth is not symmetrical is taken as proof that the earth is flat.