This question is either about etymology or language generally, as names have this feature in other languages too, but I'm just curious how the practice of naming towns in proximity to bodies of water with a built-in reference to those bodies of water came about. Obviously it's not strange to me that a town on the Hudson would be called "-on-Hudson" etc., but what "determined" or at least influenced whether a town's name ended up having a reference to a body of water as well? It's not Chicago-on-Michigan or Philadelphia-on-Delaware, so why so many "-on-Hudson" towns?
Learn English – Why names such as Hastings-on-Hudson
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Best Answer
So far as I'm aware, the normal reason for adding -on-[river] is the obvious one - to avoid confusion with another place of the same name which isn't on that particular river.
But I suppose sometimes -by/-on-sea, -in-the-moor, -in-the-dale, etc., might be used to publicise the local geography of a resort to encourage tourists, etc. It could well be that in the past, when people's water came from the river rather than the tap, naming a nearby river might also be helpful in attracting visitors/settlers.
Being British, I don't know any US place-names xxxx-on-Hudson, but I could believe that mentioning that mighty river adds a touch of kudos to some otherwise unremarkable places.
It's worth pointing out that by and large the name of a place is what the locals (and more specifically, their administrative bodies) choose to call it. Each town may have its own reasons for choosing their particular form of name, and it doesn't have to conform to any particular rules. Even granting that there might be any such rules in the first place.