After bypassing the security override and getting into the building that houses the Silent Cartographer, head right after entering the previously-locked door to trigger the cutscene. From the ledge where MC kicks the rock, you can jump all the way to the lowest floor where the Silent Cartographer is activated. You do this by bouncing off the walls (you will die some, but will eventually get it). There should be a check point nearby so you can try this over and over again if necessary. This helps particularly on Legendary mode. On the way back up you'll only need to battle the relatively easy Covenant that you would have faced on the way down.
VIDEO PROOF FROM FROGBLAST
Edit provided by g-money, Warbow & me