a dead area - you cant build cities near theses areas or on them. unless you clense the center of it from a (monster/quest/corrupt shard?)

im actually liking the idea about a corrupt shard - that when you first encounter them they are guarded by creatures drawn to its energies that also cause havok in the general area - so when you defeat it - and a channeler enters the field he changes it from corrupt - to active  (ready to be buildt on) - this makes for interesting spots on the map with large open fields of dead areas where you cant build cities untill it clears. making it even hard to secure the shards.