Crusader Kings, Europa Universalis and several other strategy games use provice based maps where "tiles" are not squares nor hexagons. Border style indicates different ranks/owner.
I've done some research and this is what I found from modding guides: they seem to use a source image to dynamically generate the borders which are used to separate the provices but also to indicate currently selected areas (border changes color or flashes etc) and Im pretty sure that same file is used for "clickable areas" (click on provice to get province details screen).
Source image contains all the provinces painted with solid colors. This image is same size as height map (water bodies and land masses) to align geographical shapes with provinces.
Then there's some sort of dictionary file (text, JSON etc) that has all the province colors that maps these colors to meta data about the province. It also makes provinces "loopable" for game engine in order to add them to in-game database and to use colors to find the correct shapes from image.
Example in JSON:
// "key" is RGB color that points to correct province in previous image
"253:28:37": {
"name": "Kent",
"otherStuff": 13
},
"142:133:150": {
"name": "Oxford",
"otherStuff": 54
}
How to create referenceable borders and clickable areas from source image?