Map Achievements (What Do People Usually Miss?)

Looking for some help. I’ve trying to get the achievements on Xbox for uncovering all map areas, and the first one i’m doing is the one that covers Serenity’s Waste, Triton Flats and Stanton’s Liver.

Places I have been to that you may think to mention: I have been down to Iwajira, I have seen the 2001: A Space Odyssey Easter Egg. Really struggling with this, as all the maps appear to be discovered.

Edit: Ok it seems to part I was missing was called Chandler’s Hole, just north of Frozen Gulch.

My best tip would be analyze the map veeery carefully for tiny areas that are actually greyed out.