Walk me through your workflow on creating an open world map

I'm interested in seeing how other people do this.

Lets say we have a 5k x 5k island. I want to create this in the best way possible. It has some hills, some lowlands, will have trees etc, and a mountainous feature in the middle.

I know that creating that as one big model or terrain is not the smartest.

So I have heard that using the terrain system should be fine. Then I've heard that it will be costly and not so good and to mesh it out. Then I have heard to use Blender and bring it in. So lots of conflicting directions...

I know you can mix and match. Especially if you have things like villages/cities or tunnels.

How would you set up a 5x5 island like this? Just use the terrain system? Use terrain and export the mesh out into blender to decrease its subdivisions and bring it back in?

Use a tool like World Machine or Gaea? (that seems like its just giving me the heightmap to bring into the terrain system and it would treat it like the terrain system - but then does it need blendered and its subdivisions lowered?)

Use a tool like Gaia to manipulate the terrain object itself?

I'm primarily a programmer so these art areas are somewhat out of my scope and am trying to learn more on how to tackle a problem like this in the sea of a lot of conflicting opinions.

 

---> U can use unity's terrain tools because it has some great sculpting tools and painting tools and with that u can download the terrain samples pack from asset store by unity which contains the heightmap brushes to quickly stamp some realistic mountains on the terrain.... u can also use custom height maps if u want by generating them in softwares like world machine or gaea. if u think unity terrain tools does not provide all the tools u need there are many tools for those stuff on asset store and github for free, the features which terrain tools lacks is that we cannot paint more than 4 textures on terrain for URP and 8 for HDRP, but its unlimited for built-in.... custom shaders are difficult to create for terrain, placement tools are very simple as they don't align to the slopes of the terrain and have very limited options and terrain tools also lack out of the box spline system to create roads and rivers for terrain...all the missing tools i mentioned above are available on github and asset store for free, i personally recommend using YAPP tool by Rowlan on github for placement
----> from my testing, using mesh as a terrain increases the no. of triangles and batches increase as more u split your terrain tor reduce triangle count which is another thing which makes mesh slower than normal unity terrain.... it also breaks the complete workflow and loose all the power of tools which terrains provide... Only benefit of using mesh is u get to use custom shaders..... Unity's terrain performs best when u use single terrain for your whole game... U need to set your pixel error to max, tick gpu instanced and set height map resolution (which also controls terrain resolution) according to your needs in terrain settings for best performance..... occlusion culling also helps in improving performance!! i still recommend you to test out performance of terrain and mesh yourself
----> i don't recommend using Prefab brush tools for placeing grass or other details because grass needs to be indirectly instanced for performance.... unity's latest versions have that but as i mentioned earlier unity's placement tools are not that great.... so instead of using the default one i recommend using GPU instancer (paid) from the asset store... it just not only indirectly instance your grass but also does it for your trees and rocks and automatically generates billboard for them which helps in developing dense forest scences easily without worrying about performance.. i recommend using microsplat shaders (paid) for terrains for performance reasons

 

Dont forget chunk streaming of the terrain. I use SECTR, hands down the best for any large terrains...