This has been discussed on the Steam boards as well. The overview map is unusable at 4k. I have tried to change the resolution and it works fine. Please fix this, I would love to play at 4k. Thanks!
Thanks for reporting this, we'll pass it on to the team.
I've found if you play around with the mouse wheel, although it flickers, you can see the different sectors. If you don't, your left staring at empty space