The WoW Atlas Addon is used to provide maps for instances in the World of Warcraft. The game was released without maps because Blizzard wanted to make instances more challenging but people being the big newbs that they are decided to go ahead and make things even easier in WoW and come up with an addon that shows the maps in instances.
If you want to take more of the challenge out of World of Warcraft that instances sometimes have, then I recommend you use this addon. Not only will you never have to explore an instance again, but you'll have access to all of the unique areas of interest that are in the instance, such as bosses or areas used for quests. You'll also be able to access complete instance information so you'll never be surprised for what to expect as far as level range and player limit.
In addition to maps of instances you'll also receive maps of battlegrounds, dungeon locations, flight paths, and raid bosses that appear outdoors.
This is one of the best addons you can get for World of Warcraft. If you don't mind never having to explore areas or learn where things are then this is definitely an addon you will want to download and install. You can zone into any instance in the game and know exactly where everything is. It can save you and your group hours and get you through instances or areas as fast as you can move through them.