This idea is just about flavour - there are no gameplay changes involved. Any reasonably-sized geographical feature should automatically get a name, visible on the tooltip alongside the name of the continent. For example, rivers, mountain ranges, lakes, deserts, islands that are three or four tiles or larger. There are two options: 1) name them randomly from a list of real-world features, so rivers could be the Nile, Orinoco, Yangtze, etc, or 2) name them based on the start position of the nearest civ, so rivers near France could be the Seine or Loire. You can change the names at any time. I think this could be quite fun for historical immersion and could be incorporated into the flavour text and notifications: "Russia has cleared a barbarian camp in the Gobi desert", "a source of iron has been found on the island of Sumatra" and so on.