Unlike the starter zones, the areas from 20-40 are mostly open to both factions. With that in mind here is your WoW Level Chart for characters level 20-40. Leveling in Azeroth is incredibly quick if you use a leveling addon. I recommend Zygor, which took me from 1-85 is just over three days played.
WoW Leveling Chart 20-40 Kalimdor
•20-25 – Ashenvale
•25-30 – Stonetalon Mountains
•30-35 – Desolace
•30-35 - Southern Barrens
•35-40 – Dustwallow Marsh
•35-40 – Feralas
Attachment 6857
WoW Leveling Chart 20-40 Eastern Kingdoms
•20-25 – Duskwood
•20-25 – Hillsbrad Foothills
•2o-25 – Wetlands
•20-25 – Arathi Highlands
•20-25 – Northern Stranglethorn
•30-35 – Cape of Stranglethorn
•30-35 – Hinterlands
•35-40 – Western Plaguelands
As you can see, the entire 20-40 WoW Level Chart takes place in Kalimdor and Eastern Kingdoms which just so happen to be the zones that were revamped for Cataclysm.
Attachment 6858
If you are an old-time player like myself, enjoy being able to use a ground mount at level 20 instead of waiting oh, so long until level 40.