World Composition with a Big Heightmap file?

Brace yourselves to a noob question! :smiley:
I started to work on a map way before look into documentations and I ended up with a big height map as my landscape (8161x8161)
Today, I was looking for some World Composition tutorials and all I can find are peaple creating new landscape and then duplicating the same, to use as different tiles of the map.
It’s possible to use World composition in a already created heightmap? Divide the heightmap into little chunks? I tryied to divide it on photoshop and then import all the 49 png chunks as landscapes, but as you imagined, it didn’t work! I cant sculpt in imported chunks and as my world is not finished, that didn’t work for me.

I am wondering this also.Anyone know?