That rarely happens in-game due to AI inheritance shenanigans especially in the early game when everyone is locked into gavelkind. So what you usually see is a mess of counties, duchies, and kingdoms spread haphazardly across the map with no regard for aesthetic value. This is what is referred to as "Border Gore".
Crusader Kings 3: 12 Best Cultural Traditions 8 Collective Lands. 7 Pastorialists. 6 Equal Inheritance. 5 Forest Folk / Hill Dwellers. 4 Audacious Cadets. 3 Castle Keepers. 2 Imperial Tagmata. 1 Malleable Subjects.
Box go to page border. Choose box and choose the style you want you can have a single line a dottedMoreBox go to page border. Choose box and choose the style you want you can have a single line a dotted line or any type of lines. Here. If you want it thicker you can go for a double line like this.
As someone else linked above border gore is basically when multiple countries on the games world map have borders that go through other borders that they wouldnt historically. Say something like Germany and spain owning parts of France while France owns parts of Germany.
From border + gore (“, bloodshed, violence”), jokingly suggesting that such borders are so gruesome they might cause someone to become physically ill.
But yea, partition means when ur vassal dies their titles will be divided amongst their kids, leaving them with less lands and subsequently less power, so a vassal that once was a threat to you, now they might not be as much.