edge
When it became common knowledge, that the world is a ball (and not a disk), the world faced its first big problem. Suddenly no one knew where to place the marginal groups. Seamonsters for example where traditionally expected near the border of the world (a feature a round world obviously misses) and today they can be found (and filmed) all around the oceans.
All the other most urgent problems of the world are of course due to its shape as well. Like overpopulation: If there is an edge there is a canonical place to add on. Or the rise of the ocean level: On a round, borderless world the excess water simply cannot flow off. Or take the global warming in general: For a disk the average temperature can easily be finetuned by simply tilting the disk against the ecliptic plane, something which is pointless for a sphere.
Even the world trade could profit from a disk world: Anything going over the worlds border could be made liable to customs duty.
Maybe its time to put the world over the edge.
footnote: the mathematicians of course have already a solution for that up their sleeves: Using a suitable metric a cube makes a good sphere as well. However, this solution would make the profession of a cartographer a rather dull job if not even practically dispensible.