Terrain in Unreal Engine created from OpenStreetMap and SRTM data.
What you’ve got in the image is 30 minutes of latitude and longitude, i.e. half a degree. We call this an M30 segment. M=Minutes - so M30 is 30 minutes.
Each M30 segment contains 3600 smaller segments, each covering 30 arc seconds. So we call these AS30 segments.
We can churn through about 600 AS30 segments in 12 hours so a complete M30 takes three days.
At this rate we could complete the world in 628 years!
It’s an ellipsoid world so there is a proper horizon and all the OSM buildings are in there, point features etc. Essentially it’s 3600 FBX meshes all joined seamlessly together.