This is actually pretty similar to a post I did a bit ago.
I understand the point that other fellow was trying to make, namely that a theoretical model can be put forth to establish his point. That it is not EXACT does not invalidate his point. The idea is that it is an approximation, and will be until someone actually goes out, from the Flat Earth Society, and makes a map of it.
That said, if you look at the map, and consider aerial navigation for this issue like we originally were, what we have here is a point of distance traveled over time traveled, basic velocity. The point that was being originally made, is that if you travel point A to point B on that map, you will have traveled a set distance, and in a set amount of time. If you complete the circuit around the circumference of that circle, you will reach your original destination.
Let us assume that these two points are very close to the outer rim of the map, say South Africa to Argentina. Travel from those two points, going around the circumference of the circle. Perhaps add Australia to the list to make it a full circle with three established points. Now let us say that you travel a bit north, or in this case, towards the theoretical center of the Flat Earth map, a location that can be agreed upon even if the map is an approximation. Chart out three new points along this circle, going around the North Pole. Let us say from Brazil to Japan to Hawaii and back to Brazil. These are both well traveled and well documented distances and times traveled for circumnavigation. For the Earth to be flat, the distance of the circumference of the second flight route would need to be less than the distance of the first. It is in fact well documented, on a near daily basis, to be greater.
Would this not show that the Earth's circumference is expanding as you go from the outermost parts of the map to the Equator, not receding as the flat map shows?