About Land and Water question!

I've made a custom map, so the land and water bodies are different from the default. My question is: how do I set the map to tell the difference between what is accessible to only naval (water zones) and what is only accessible to ground units (land)? is it possible to have land that is not within borders i.e. not owned by any country, but just is there?

Everything inside your borders is considered land; everything else, water. The default when you draw borders is not belonging to any country, so if you just draw borders anywhere, you'll have achieved your second goal.

Okay thanks!