My Latitude Vapor arrived today, and I can't quite figure out what this pocket is for. It looks like a perfect spot for a hydration pouch, but there's a sleeve inside the actual pack for that as there is a port for the tube to feed through. This pocket is outside the pack but sandwiched between it and the back cushion pad. Is this a common feature on packs? I've never seen it before.

I believe this is a holdover feature from the first generation of Granite Gear's Vapor suspension. My first Vapor Trail had no internal hydration sleeve. Instead, they advertised the hydration sleeve as being external to the main pack bag, behind the back pad. I never used it as such, but I do remember some ancient comments on this board (or another?) that liked the design: it saved the poster a wet sleeping bag when his hydration system leaked, and the water ran down the back of his legs instead of inside his pack.

When they added the internal sleeve, they quit advertising the external feature but kept the same design. I had some modest success using it as a map pocket; usually, the map didn't slip all the way out of reach.

That's where you put the Platypus Wine Bag.

Glenn nailed it. Granite Gear has decided to keep it in their packs because it doesn't add any weight, it's a feature that many think is a big benefit and gives them hydration options, and it's unique to Granite Gear packs. I like it for hydration because I don't have to pull everything out of my pack inorder to access it. However, it doesn't do so well if you've really stuffed the pack. Luckily the Latitude Vapor is light enough that you could justify using it as a day pack and this is where having this external 'pocket' shines.

I love your pack! It is my go to pack for most of my backpacking. It's super comfy, gives me a few more options than the Vapor Trail, but is incredibly light. I hope it satisfies your needs as it has mine...

I'm stoked to try it out...my next trip with the group isn't until mid March so I have to wait with this thing just hanging in the closet, taunting me