I'm at 32/35 for the Challenge MT Space (Visited every location in the Big MT).
Problem is, I don't have any more unexplored locations showing up on my pip-boy radar. I've been to all the ones I have found, and done 360° sweeps, with no new arrows appearing at any of them.
Are the last locations inside, or accessed through another location (in one door out the other?), or do I just have to run round the crater looking for arrows to pop up?

Cheers.

There are a few locations that are troublesome, the arrows for them may disappear from time to time, it was the same in Honest Hearts, all you can do is check areas that seem suspiciously devoid of markers.

I'm having this problem too. I haven't found Ulysses Point and apparently there's a place where Christine stayed that I haven't found. I found Elijahs watch ok, just not these other locations.

http://fallout.wikia.com/wiki/Old_World_Blues_(add-on)

Use the locations list.

They should all have maps by now.

Awesome, thanks for the tip!
Compared the list to my Pip-Boy map and found the Loading Station, Signal Hills Transmitter and Elijah's Watch are the one I need to go visit.

@Heinous
Ulysees' Point is about 100m NW of Higgs Village Entrance. The Christine hideout near Little Yangtze isn't a 'tagged' main location.

Ulysses Point is where Christine stayed.