Game like eu4, how to create a map?

I will create an interactive map like in the Eu4 game. I am thinking of making the borders of this map 1 pixel, will this be correct and how can I create this map in the fastest and most effective way? I thought of creating it using a ui button, but in this case, I did not know how to put the cities on the map side by side, they may overlap and block each other. I am waiting for your thoughts and suggestions on this subject.