Here's the second step of my map making process: "hexagonisation" of the base map.
However, before that I actually went and added Shetland Islands to map: its exclusion on yesterday first draft had been nagging at the back of my mind for the whole day. It doesn't feel right that they aren't included.
I didn't include it because I wanted to have as much land as possible given the number of tiles suitable to a Huge map. Now I've added it, the whole map has become bigger than Huge, which means there could be performance issue. (You know how crash-prone the game could be...)
The solution is to add an option to disable the top 14 rows to make the map conform to the proper Huge size, so people with a more powerful machine and a love for the Shetland Islands can enjoy the full map, while others can enjoy the map as I originally imagined.
Next steps: adding rivers, mountains & hills