These routes were made with the routes addon, they use GatherMate to find the nodes and are then clustered to 60 yards and optimized using the "extra optimization" option.
This means that what you're seeing is the optimal route for mining according to the newest update from GatherMate.
For cobalt, Zul Drak is your best bet.
Storm Peaks is an alright route but the mountains start to piss me off royally.
Sholazar is great if you don't have much competition.
Wintergrasp is great if you don't have an epic flyer because everyone has to mine on their 100% mounts. I still go WG but only when there's a battle on, lessens the competition by a lot.
Icecrown is still my favourite place to mine, I just love it!
I made this so that people would know where to go in Northrend by just looking at a single post. It's annoying having to scan through multiple posts looking for a map for each zone. Pick the zone which you can stand to farm for the longest time in and make sure you don't have too much competition. Feel free to request a map of a zone you need and i'll do my best to make you one.
Good luck with your mining,
Denbob