This source simply references where this map came from. I usually don’t find a citation necessary; I just attach the map to the place record and that’s enough. Its references are sufficient. Sometimes I might only take a piece of the map and then I might add a citation explaining why there’s only a portion of the map.
I attach the note to the object, here the source, on which I want to work. I only link to this object when it is only a working reference.