You can use Nitrogen to generate a map bigger than 16K, but neither the server nor the client will load it. There is a hard coded limit of 16K.
I have used Nitrogen to create a 20 K map. It took a while but did not take that much memory. Haven't bothered with anything bigger cause like I said, the game itself will not load anything bigger than 16K.
Under Linux, the file UserOptions.ini says:
This file is no longer used for overriding settings. All 7 Days To Die settings can be
found and changed in the file:
~/.config/unity3d/The Fun Pimps/7 Days To Die/prefs
You can directly open the file from the game launcher on the tools tab.
On a Windows system, the file says:
This file is no longer used for overriding settings. All 7 Days To Die settings can be
found and changed in the registry under the key:
HKEY_CURRENT_USER\SOFTWARE\The Fun Pimps\7 Days To Die
You can directly open RegEdit on that key from the game launcher on the tools tab.
<sigh> Why do people do this? The Windows registry is a horrible kludge and one of Microsoft's biggest mistakes. FWIW as a software developer, when I worked on Windows systems, I refused to store stuff in the registry. But I digress....
Neither the prefs file nor the registry contain information on world size. That is found in rwgmixer.xml, which is found under the steam 7d game install directory:
... steamapps/common/7 Days To Die/Data/Config
However, setting the world sizes there to 16384 doesn't work, the game ignores it.
AFAIK you can't directly generate a 16K world from the client without first creating a 16K template (like with Nitrogen) and putting it in your GeneratedWorlds directory. I know that works because I've done it many times.