Riverboats and MC Ecsher

[Chon Waen]

@irrelevant
Yeah, all of that. But mostly the last.

[A Nonny Moose]

It is much more likely that the river is a Moebius strip.  At the edge of the map, the boats enter the twist and emerge from it upstream.

[salamander]

Now it's clear -- the Bannies are Greek.  Early Greek mythology held that Ocean was a stream that flowed around the edge of the world.  The sun would sink into the Ocean stream in the west, be carried around the north edge of the world, and re-emerge in the east.

Traders have learned the same trick ... or maybe they're gods.

[rkelly17]

It's very simple. Your world is flat. It has edges and corners. You get to the edge, you fall off.

But even a flat world has another side. What's on the other side? My world.

The merchants bringing you stuff? They just came from my TPs, on the other side of your flat world, bringing you the stuff the stuff that I just traded away. Enjoy!

Oh, and please be sure to send good stuff back, okay?

I would say that @irrelevant is partially right. The Banished world is, in all likelihood, a cube which appears flat to each side of the cube. He and @Chon Waen inhabit opposite sides of the cube. When the merchants exit @irrelevant's world they enter an alternative Banished world in which people import ale and export fruit. The merchants then exit that world and enter @Chon Waen's world where they trade the fruit for ale. Etc., etc., etc. There are two sides of the cube that are just there to hold it all together and produce neither fruit nor ale so are--actually--irrelevant.

[A Nonny Moose]

Let imagination know no bounds.

Maybe Banished exists on the event horizon of a black hole.  The merchants can't be lost due to the preservation of information, so when they transit the no-time, no-space they have to come out near the headwaters of the river.