Like Shell Man said, Oddworld is ten times the size of Earth in terms of diameter, giving it a total surface area of the same proportion. This clearly gives OWI a massive space to work with! In comparisson, all of Oddworld we've seen so far is in Mudos, a country the size of Nicaragua.
The Map was made by Alf's pal Buddy, who consulted a Slig while creating it, and was so distraught by our unhappiness with it that he went on an eating binge, but fortunately has recovered with thanks to an intervention from Abe and the South Meech Diet.
