Archaeology

Here's what you should expect while leveling, based on my own experience leveling to 525 and then going for achievements.

• You get one skill-up for every set of fragments you loot, five skill-ups for every common artifact you solve, and fifteen skill-ups for every rare artifact you solve until about 100.
• At 100, you'll stop getting skill-ups from collecting fragments, making the five and fifteen skill-ups from solving common and rare artifatcs the only way to level to 525.
• Archaeology can be leveled anywhere or anytime you do it. You don't have to move on to higher level continents to continue past 300 and 375.
• Digsite locations are fixed and always spawn nearby matching doodads and environemnts. That is, night-elf sites are always nearby night-elven ruins, fossil sites almost always are surrounded by several half-buried fixtures of bones, vrykul sites are always found in active vrykul villages, etc.

1 - 300

• The first big chunk has to be done in Kalimdor and Eastern Kingdoms, excluding Cataclsysm zones. Digsites in Outland won't spawn until you reach a skill of 300. Similarly, 375 for Northrend, and 450 for Cataclysm zones.
  
  Kalimdor has mostly night-elve digsites; they're the most common by an enormous margin and can be found all over the continent. Fossils are the next most common, but they are found almost entirely in the southern half of the continent. There are only four or five troll digsites, and all of them are in Tanaris. Lastly, there's a single dwarf digsite at Bael Modan in Southern Barrrens. If you level in Kalimdor, get ready for night-elf after night-elf.
  
  Eastern kingdoms has a combination of dwarf, troll, and fossil digsites. Troll and dwarf digsites both have a strong presence all throughout the continent and you should expect to find a more-or-less equal amount of both. Fossil digsites have about the same availability here as they do in Kalimdor, although their digsites are more spread out.

300 - 375

• Digsites in Outland become available once you reach a skill of 300. Outland is actually a pretty nice place to level because it's the smallest continent, it has only two races: orc and draenei, there are no digsites in Blade's Edge, and all of the artifacts have at least two keystone slots. The only downside is that common artifacts here take 45 fragments, up from the 30-36 it takes for the 1-300 types.

375 - 450

• Digsites in Northrend become available as soon as you reach a skill of 450. Northrend has nerubian, troll, night-elf, and vrykul artifacts. There are vrykul digsites in Northrend like there are night-elven digsites in Kalimdor: they're everywhere and odds are they're all you'll be digging up. Troll digsites in Northrend aren't uncommon, but they don't have anything close to the presence of vrykul. Nerubian digsites are sparse and spread out across two or three common areas. Surprisngly, night-elf artifacts are actually pretty uncommon here.

450 -525

• At 450, digsites in Kalimdor and Eastern Kingdoms have a chance to spawn in the new Cataclysm zones, that is, Mount Hyjal, Uldum, and Twilight Highlands. Unfortunately, they share the same four digsite maximum with the rest of their respective continents. Uldum has only tol'vir digsites, and tol'vir digsite spawn only in Uldum, making tolv'ir artifacts sort of hard to come by. Mount Hyjal has even more night-elf digsites, and Twilight highlands has a bunch of dwarven digs. Deepholm and Vashj'ir do not contain digsites.

Happy hunting.

Artifacts fall under 9 categories:

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• Dwarf - Requires level 1 Archaeology | Sites in Azeroth
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• Fossil - Requires level 1 Archaeology | Sites in Azeroth
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• Night Elf - Requires level 1 Archaeology | Sites in Azeroth
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• Troll - Requires level 1 Archaeology | Sites in Azeroth
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• Draenei - Requires level 300 Archaeology | Sites in Outland
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• Orc - Requires level 300 Archaeology | Sites in Outland
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• Nerubian - Requires level 375 Archaeology | Sites in Northrend
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• Vrykul - Requires level 375 Archaeology | Sites in Northrend
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• Tol'vir - Requires level 450 Archaeology | Sites in Cataclysm
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Night Elf digsites can aslo be found in Northrend with about the same frequency as Troll digsites. By my count there are only 5 Nerubian digsites: 2 in Borean Tundra, 1 in Dragonblight, 1 in Icecrown, and 1 in Zul'drak.