I'm gearing up to send out the first batch of prints to Epic Hero patrons, and it turns out that I need to have the maps formatted for A3 paper size (42 x 30 cm or 16.5 x 11.75) to get them printed. Since I've been working based on the assumption of US Letter double page spreads (17 x 11 inches, or 43.2 x 27.9 cm), this means some reconfiguration to get things to fit.
First I had to trim the left and right sides. Luckily, this is a very minor thing, and I had left enough space that it doesn't really matter.
Next, I had to add an extra 2.1 cm of vertical space. This is potentially far more problematic, though in Narwan's case I was saved by the sea at the bottom of the map, which is very easy to expand.
The final map looks a little less cluttered than the double US Letter version, thanks to the extra sea at the bottom.
You may also notice that I've removed the border around the edge of the map. This is because it sits right at the edge of the bleed zone, and therefore would likely get trimmed partially on some sides while not reaching to edge on other sides. In other words, borders are best avoided when it comes to printing.