Distances in the South
The topic of Distances in the South is a topic of great interest to the Flat Earth Community, as its proposed models predict that the lines of longitude south of the equator will either converge or diverge. According to multiple-pole models with an Antarctic continent the lines will converge (See the Bi-Polar Model). According to the classic Monopole model with an Antarctic rim the lines will diverge.
Sea Travel
On the topic of sea travel, we find that sea travel in the South may have been historically difficult.
Air Travel
There are several potential variables and issues in analyzing air travel for accurately determining the geography of the Earth under the various geographic models in discussion.
See: Issues in Flight Analysis
General Interest
Although this subject is of high interest to distinguish between the models, it is also one of the most neglected subjects, as Flat Earth advocates tend to focus their energies on things they can see and test. On this subject we cannot see or test the matter and can only infer geographic, oceanic, or atmospheric properties based on disperate data.