Shortcuts in the main facility

Expanded June 20th 2014

Within the main facility there are various vertical shortcuts you can take on your way down to the Cartographer, for speed or stealth or just a bit of variety. Shortcuts can also help you bypass enemies, and you can tackle them on the way back up instead. Note: all my advice here is based on the PAL Xbox experience. The situation for NTSC/PC may differ in regard to possibilities and fall damage.

Plenty of options from here

Falling from the cutscene platform

Just through the security door which needed unlocking, turn right. In that direction a platform sticks out and a cutscene would normally get triggered, after which a checkpoint is due. But if you throw a grenade into the void shortly before hitting the cutscene trigger, or if you do some firing instead (any weapon can suffice, and even the presence of a single needle in the air will do), it usefully cancels the cutscene, allowing you to skip straight to the checkpoint, which you may want for safety.

Down in one go!

From the platform it's possible to make one or more falls to reach the area where an overshield is located, just around the corner from the Cartographer. There are multiple ways of doing it (and bear in mind that it's possible to leave the platform on either side), so I suggest you do some exploring to check that out.

It can be done while maintaining full health even without an overshield, if your landings are well cushioned (crouch as you hit). With an overshield however, you can simply make one big fall straight to the bottom if you don't mind losing the overshield. Alternatively you can preserve almost all your overshield by using a sequence of smaller well-cushioned falls.

Into the drop-hole

Drop-hole in the upper room

At the back of the upper room (the room where an Elite seems to be operating some device), there's a well-hidden hole in the floor that lets you drop down to a spot outside the Hunter chamber. It's a sneaky alternative to using the ramp, and gives you a nice way of taking a few Jackals by surprise, or bypassing them entirely.

When you fall down, you'll initially be under cover from any Jackals, which is nice. But for stealth, it's good not to get spotted in the upper room, else the Jackals will get alerted too.

Let's hit that slope

Big drop after the Hunters

Just past the Hunters, a walkway starts to lead you down. But after that first short slope, look down. There's a drop that looks too big to survive, but you can make it without any health loss if you land on a small bit of sloping surface at the bottom; you don't even need an overshield. Slope helps break your fall; it's less of a shock to the system.

You may or may not get spotted by a patrolling Grunt when you land. The Elites guarding the Cartographer are just a short way off, around to the right down a ramp, and you'll have the opportunity of taking them by surprise if you don't get spotted by a Grunt.

Off the edge outside the Hunter chamber

By the supplies outside the Hunter chamber, there are various ways of dropping down. If you've got an overshield you can fall all the way to the bottom floor where there's another overshield. You can also get down with no damage to health (or overshield if you've got one) by making a few lesser jumps. And incidentally, if you've already been down and you bypassed enemies on the way up, you could now jump a few feet down onto a ledge on the left, and potentially surprise some enemies below.

Update: Falling onto the overshield

Qazitory alerted me to another possibility, in the case where you have no overshield. You can potentially survive a massive fall by landing on the overshield down there. A fall from where though? The platform? On my PAL Xbox, I was unable to get enough distance to actually reach the overshield from the platform, unless I boosted myself with a grenade going off behind me. But on NTSC/PC you have slightly higher running speed, so maybe you can reach the overshield without needing that boost? The highest place from which I can drop onto the overshield is the edge of the Hunter chamber. But it's quite tricky to aim yourself, and you can easily end up getting nudged out into the void. Also it seems like you have to really hit the overshield well, or you may die without it activating. While trying out this fall, I also noticed that if I hit the edge of the purple container (ideally with a crouch I think), it was possible to survive without hitting the overshield.