Add Terrain - Imports a terrain mesh to the scene which you can modify after you selected it as the terrain property.

Subd Render / Viewport - Resolution of the mesh in rendered or viewport view.

Scale - What you expect when scaling other objects using the “s” key. Only use this property when scaling terrains and NOT the “s” key.

Location - changes the location of the texture coordinates and NOT the location of the object itself in the scene.

Scale (coordinate transform) - changes the scale of the texture coordinates and NOT the mesh itself.

Z-Rotation - Rotates the texture coordinates along the z-axis.

Edit / Apply - toggles the editmode in which you can add / remove / adjust heightmaps and masks. In editmode heightmaps are only visible in the rendered view.

Default Library / Custom Path - Decides whether you want to add a premade heightmap from the default library or you want to add a custom made heightmap.

With an added heightmap selected, you can edit following properties attached to it:

Clamp X / Y - Clamps the texture coordinates which are higher than 1 or less that 0.

Extension - The pattern in which the texture is mapped to the texture coordinates.

Interpolation - Process of smoothen the area between pixels with different values.

Mix Operation - Decides which calculation the current heightmap layer performs on the layer beneath