[danzig70]

I looked at mods such as the additional harbors mod and the milk cow mod to determine which files needed to be edited. I was adding bases though for use by my sub.

If you create a custom mod folder in the mods directory you can place just the files you want to customize and use JSGM tool to enable the mod. That way you wont have to alter any original files. Its helpful for troubleshooting.

There is a field for "show on map". Is that marked to "True"? If it shows up in the editor, it should show in game when you zoom in to it.

If you are just adding cities without bases it should be straight forward. For "File Name", use the location .dat, .tga files that matches the city best. A pacific island could use, "small_pacific_city (.dat, .tga)". Its called something like that and these files are in the /terrain/locations folder.