Create a SCR_MapEntity (not MapEntity !!!)
open the "Map Export" Tool
Go to the Map Tool Export Tab
Export "Geometry 2D" -> creates a .topo file (Warning: can take very long and a lot of RAM, don't try to export Everon)
Export "Rasterization" for a "Satellite image" of your map -> creates a .tga Image File
Right click the .tga file in Workbench and select "Register and Import" -> .edds Texture File created
Go to the SCR_MapEntity and set the Map Geometry Data to the .topo file and set the Satellite Background Image to the .edds Texture
Please let me know if this worked for you, or if any problems arose 🙂