Thanks for the comments.
Fist off I made a math error in my initial post, the terrain is 12,500 square kilometers, not 25,000. It’s still very large though.
In answer to the comments yes, it is tiled terrains. The height maps are created in World machine. The tiles are fairly low resolution (I wasn’t sure if my machine could handle any higher.) They are 505x505 pixels and although there are a few spots in the terrain that the low detail can be noticed the overall result looks good so I’ll probably proceed without importing a higher res version. I set the tiles to be 8 kilometers square (14 by 14 tiles for a total of 196 tiles in engine) and I positioned the world extents and tiling in world machine so that the corners sit precisely on the world machine grid. This is so that if I choose to down the road, I can generate further terrain tiles and add them to the existing world fairly easily so long as I keep good notes on the initial import offset and scaling in Unreal.
I should mention the textures are entirely procedural, using “MaxStudios” amazing ‘Automatic Landscapes - Deserts’ procedural texture tool from the marketplace. With a little technical help from MaxStudios I was able to plug Unreal 4’s landscape grass output node into the various textures on the terrain and get very realistic procedural generation of the foliage over the entire terrain. In fact none of the vegetation in the screen shots is placed by hand, it’s all generated per the textures, which was another one of the goals I set for myself in this experiment. It even varies the foliage based on it’s position in the terrain. ie. brush and grass in the hills, widely scattered small rocks and pebbles in the salt pans, all without me painting a single stroke. There was simply no way I was going to be able to hand paint foliage on a terrain this large.
As far as my rig is concerned it is a modest machine by any standards. And AMD 3.5 GHz CPU, 16 gigs of RAM, and an NVidia GTX660 GPU. Last I checked in Unreal my frame rates were in the 30s and 40s in the editor. Granted this is with just the terrain running. I assume that as I begin to add complexity in specific set pieces, characters, AI, gameplay related blueprints, etc… that I will need to optimize. Only time will tell how Unreal handles it once the game part starts getting more involved.
Thanks again for the comments.