Aligning Plane and Terrain

Hi...noob question.
I'm setting up a plane and a terrain in my scene.
Couple of beginner issues.
1. The center point of the plane is different to the center point of the terrain when I add them to the scene, even though they are both at position 0,0,0. I want them to appear in the same place.
I can just pick one and move it but that seems wrong. I feel like they are referencing a different meaning for 0,0,0. Do I need to set some kind of local vs global position ?
2. The plane and the terrain have the same Y position in the scene so they sit at the same height and they sort clash and jump in and out of view. How do I make the plane show above the terrain without changing the Y position ?
I can pick one and make the Y position slightly higher or lower, but that feels a bit clunky and then I have to line up all of my other assets with the new positions.
Thanks in advance.
Anthony.

 

1. It's just the object's position origin. Terrains are at the corner and planes are at their center. You need to work around that. Just move the Terrain so it's center is at zero if that's what you want. You could make the Terrain a child of an empty GameObject and re-center it to that and position with the GameObject.
2. When two object's surfaces are on the same plane, either can be displayed as the one closest to the camera. This causes the textures to flicker between the two. You will need to lift one above the other so the topmost surface is not ambiguous when rendering. It may only need to be 1mm or so for typical scenes.