I’ve done exactly that about six years ago in Ogre3D with C++. Now I’m about to port it into UE4. Will tell you when I’m finished. By now, you can look my source code here (look for the functions drawLevel4 and readLevel4Rec.
If you’re still looking, there are now some plugin tools to UE4 tools to help you use ESRI shapefiles and OpenStreetMap data to create things like landscape splines for roads and rail etc… www.terraformpro.com