The project above is currently on hiatus because I'm currently working on a mod based on the Total War: Shogun 2 game. The mod is supposed to take place mostly around the North Sea around 1200 AD.
For now, I'm basically preparing the job, mostly working on the map itself. Note that the following stuff is just a draft that will be used to create the necessary files for the game.
My first task was to find a map of the area with a very high resolution as the game uses something about 16384 x 8192 pixels. I've finally ended up with the Advanced Land Observing Satellite (ALOS). You need to register (for free) to use it. It gives you access to a world map, itself divided in square areas, themselves divided again in squares. I've just save the pic of each necessary square and then I've merged them with Photoshop (410 in total). Note that I had to compress it a bit. Here is the result:

 
--- click on it to enlarge


But that's a map showing the North Sea nowadays. Actually, the coasts lines were different at the beginning of the 13th century. After some researches, I've modified it, mostly the Kent in England and all the Frisian coast (from Netherlands to Denmark). I think that I should be quite close to how they look like in reality at that time:

 
--- click on it to enlarge

Note: I've implementented the lakes but still have to do the rivers. That's the downside of ALOS unfortunately.

If you spot any mistake, please, let me know.