I'm quite new to OSM data. Can anyone help me with the best tags to use to identify major shipping ports? I'd like to be able to identify cities that have a significant amount of commercial shipping activity. I haven't found this as specific tags, so maybe I need to use something else as a proxy for shipping activity. I don't know - something like cities that are harbours and have customs and a lot of docks and cranes, etc etc.
I'd love something a little simpler, if you're able to help.