Thank you Jason, very much.
Yes, I’ve tried that, but the thing is, I need to import an area of approx. 450x200km squared. And since it’s quite big, I thought it would be better if I just import it on the go, as I will work on the map, tile by tile. I’ve tried to import tiles, e.g. map_x0_y0,map_x1_y0 . I can join these two. Then I’ve imported map_x0_y1,map_x1_y1, again, those were joined nicely, but I was not able to join or smooth over the first two landscapes.