Thanks Rabinoz!
Found this page on the Wiki,
http://www.theflatearthsociety.org/tiki/tiki-index.php?page=Eratosthenes+on+Diameter
It mentions 12,500 nautical miles ...
Is your figure also nautical miles?
No. They both should be "statute miles".
Eratosthenes on Diameter
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We can use Eratosthenes' shadow experiment to determine the diameter of the Flat Earth.
Syene and Alexandria are two North-South points with a distance of 500 nautical miles. Eratosthenes discovered through the shadow experiment that while the sun was exactly overhead of one city, it was 7°12' south of zenith at the other city.
By sheer math, 7°12' makes a sweep of 1/25th of the FE's total longitude from 90°N to 90°S (radius).
Therefore we can take the distance of 500 nautical miles, multiply by 25, and find that the radius of the Flat Earth is about 12,250 nautical miles. Doubling that figure for the diameter we get a figure of 25,000 miles.
The earth is physically much larger, of course. A circle with a diameter of 25,000 nautical miles across is simply the area of land which the light of the sun affects, and represents the area of our known world.
I would assert quite strongly that the "nautical miles" in the above Wiki entry is incorrect.
If you want to be precise, Alexandria (at 31.2001° N, 29.9187° E) is not quite due north of Aswan (at 24.0889° N, 32.8998° E).
The slant distance is 843.4 km but the
North-South distance is 790.7 km and the latitude difference is 7.11°.
The end result turns out right with a diameter of 40,029 km or 24,873 statute miles.
This rounds to the 24,900 miles for the diameter of "known earth" in "the Wiki".So, I'm sure the "nautical miles" in the "Eratosthenes on Diameter" is a simple mistake.
Also, what is the “bi-polar” map, it looks more like a traditional globe map ie with the Antarctica as a continent but i thought the FE idea was the Antarctic is around the whole circumference. Can you clarify?
I'll let sandokhan or Tom Bishop, who supports a similar map, handle that.