Making map_heights and map_regions correspond

So I've been searching all the forums and so on for a guide on creating a new campaign map, but from the looks of it, there isn't a definitive answer on making the heights and regions map correspond. Does anyone have a trick or tip to make sure the land mass and region map correspond?

Also, since ocean is based on the blue values in the heights tga, can we just make the entire ground_types .tga file just one ground type for testing purposes (like all high fertile for the entire map?) or do we have to designate ocean in it as well.