When tring to enter the building where the cartographer is, Cortana says <'hurry...">. At this point it is possible to get through the doors before they close!
All you have to do is drive (on a warthog) as fast as you can towards the doors and simply jump out just as you get there. It may take a few tries, but it is possible.
Strangely the golden elite with the blue sword that is beyond the doors will not react, even if you shoot at him.