Take a map, lay it flat on the ground.
Lay a grid of lines over the map.
Those are your X,Y coordinates.
Any location can be found by going across the lines to the appropiate X and moving up the lines to the appropiate Y.
WoW's NPCs (and static items) are located at certain grid points (coordinates) on the maps.
Titanbar, and other such programs, will show you what X,Y you are at. Then you just need to move to the X,Y the NPC you want is at.
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Omusa - 66 Tauren Hunter - Illidan
Diafp - 17 Blood Elf Mage - Illidan
Seoman - 70 Dwarf Warrior - Anetheron
Seomusa - 26 Draenai Shaman - Anetheron
"Americans just aren't gullible enough to believe that they came from a fish," John Morris, president of the Institute for Creation Research in San Diego