16k map will break atm as far as I'm aware. You might get it created, but it disconnects the client before they finish getting the map data, and ends up crashing the client.
I did try expanding a map by creating the larger map, and importing the non-rad regions, but it's borked hard. Will need to test on something less experimental.
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Oh and max map currently stable is 8k. larger is not advised, but theoretically you could make a 12k or 14k map. I know at 16k it breaks. tested extensively on that one.