In Crusader Kings II, each noble has a "home base" of sorts: it's where their coat-of-arms appears on the map. When you're a ruler, your vassals are more likely to revolt the further away they are; it's hard to hang onto Jerusalem if you're the King of England.
I'd like to reduce this penalty for distant vassals by moving my "home base" to somewhere a little more central. (Eventually, of course, I will conquer the world and then move my capital to somewhere central like Venice. Mwahahaha.) How can I move my home base? Alternatively, how can I move a vassal's home base to somewhere closer to me (so that Jerusalem stops revolting)?