How to combine meshes seamlessly?

I'm trying to combine tiles of simple unity planes into one single mesh by following the unity3d's scripting manual. The problem is when i apply a heightmap to the final mesh seams are visible. Is there any way way to avoid that? thanks,

I think your trouble is that while `Mesh.CombineMeshes` will put all your geometry into a single container, it does not actually modify the geometry (ie: doesn't replace overlapping vertices with a single one).

You either have to do that manually, or use software like StitchScape.

If you don't want to pay for a program, you can use a 3D modeling software to make your own terrains, and then you can make it as big/small as you want...