Ok, I will post here one picture, not from me (from other user), but same problem I have.
How to deal with this sharp edges on landscapes?
I guess I must do something with tiles, but what?
Can’t figuread out what.
Thnx!
Where’s the picture? 
oh yes, this picture like Chariots said 
I tried everything with landscape tools, but no effect. Sharp edges is still there.
I didnt import height map, I juct created own map via landscape tools.
You should be having 1 vert per meter. You can use the smooth tool. Basically smooth your topology a bit. You can’t subdivide the landscape to get smoother result.
Ok guys, thanks a lot, I will try this.