I think you got in the border vector territory, the pros are that if you get it right you basically get the greatest borders of them all. The downside is that it is super complicated. I plan to tackle this as well sometime in the future, when I have some time off from university work. Your best chance is to try read the docs from oikoumene and implement it yourself.The latest link will get you to their explanations of their algorithms, I wish you best of luck and keep me updated if you manage to implement their approach.
Viewing post in Grand Strategy Map Demo comments
Well, my approach here is based on shaders via images and I am using an the HQX upscaler. The ideal way to do it is via vector graphics, the kind that you can infinitely zoom in and they never look blocky. Think of .svg and I hope you get what I mean. I wish you luck, I am currently working on university related things and I had to postpone my grand strategy endeavors temporarily. I would like to make an implementation from scratch at some point and make it public.