Need help with creating huge terrain

Development World Creation
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Hi, I’m trying to create a big terrain (100kmx100km) in UE5 and having some trouble.
I use an external program to generate png heightmap (single or tiles). Then I try to load this heightmap into Unreal. If I import even 25’000x25’000(one sample per meter) png directly as terrain, the editor crashes saying that there’s not enough memory(Ran out of memory allocating 564024 bytes with alignment 1. Last error msg: The paging file is too small for this operation to complete…).
Then I scaled down my operation a bit and tried with a 10’000x10’000 map. This time the file was imported, however the terrain is flickering when looking around in the editor/playing the game. Sometimes the whole terrain disappears and other times only small chunks are missing. It seems, that collision is intact and it’s just some visual bug. (example: flicker — ImgBB)
And when I manage to load an even smaller heightmap(1000x1000 pixels) as terrain, it appears to be blocky(example: blocky — ImgBB) with noticeable bumps. Also, the borders of terrain components are sometimes visible as empty spaces between parts of the terrain.

My process is this:

  1. generate png (2 or 3 channels, doesn’t make a difference as far as I can see). Here I get a warning that png is not grayscale, however I’m sure that it is, in fact, grayscale (example: noise-x0-y0 — ImgBB)
  2. in “empty open world” level template create sky light, atmospheric light and sky atmosphere.
  3. open landscape menu with shift+2, there “import from file”, leave all settings intact. press import

I’ve looked at several tutorials and read parts of the documentation, but currently don’t have the understanding of what am I doing wrong. I’m new to Unreal, so I could have missed something obvious)

In the end, the question is this: how do I create smooth 100kmx100km terrain in Unreal out of heightmap without holes and flickering? What am I doing wrong?

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For now, I’m loading one big file 8129x8129 pixels as recommended in the documentation. Sadly, this means that terrain has very low precision: 1 point for every 12 meters.

I(mostly) solved flickering problem by checking World Settings → Advanced → Enable Large Worlds. Sometimes part of the terrain in the distance may disappear when playing in the preview, but it appears back when I come closer.

The problem with empty spaces is not present when loading terrain as one big image.

Remaining questions:
is it possible (and if yes, then how) to create detailed 100km x 100km terrain? Ideally with 2-4 height points per meter.
How to get rid of blocky terrain without using smooth brush on it(this is not viable due to the scale of the terrain)?

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Sorry for late response, but I see no world settings> enable large worlds , anywhere, perhaps in different area. Im also seeing very weird , inconsistent flickering in various ways, of terrain, either moving around world, or in edit mode;.