Daniele Please let me clarify, you don’t know the exact location, just something broad like “Somewhere in New York”, correct? And that what you would like to assign as location to the photo?
The thing is, location data in photo metadata is defined by coordinates, there is no place for a name. This is not what we invented, this is how image metadata work. And if you want it to be displayed on the map, the best aproach is to set aproximate location, such as New York City center, even though it probably happened several miles off.
If you don’t actually care about displaying this on the map, then you should just use comment instead. Write there anything you want.