Levels of Zones

Eastern Kingdoms: http://www.wowhead.com/?zones=0#0+2+4
Kalimdor: http://www.wowhead.com/?zones=1#0+2+4
Outland (Burning Crusade): http://www.wowhead.com/?zones=8#0+2+4
Northrend (Wrath of the Lich King): http://www.wowhead.com/?zones=10#0+2+4
Pandaria (Mists of Pandaria): http://www.wowhead.com/zones=12#0+2+4

b. Levels of Dungeons (instanced area that a small group can enter - usually 5 or fewer)

http://www.wowhead.com/zones=instances.-1#0-2+4

c. Levels of Raids (large scale instances designed for10- and 25- man raids)

http://www.wowhead.com/zones=instances.-2#0-2+4

d. Levels of Battlegrounds (instanced areas where you and members of the same faction compete with members of the opposite faction)

http://www.wowhead.com/?zones=6#0+2+4

e. Scenarios (instanced areas where a very small group of players complete an objective)

http://www.wowhead.com/zones=instances.-3