In general the world of Myaasia has an overbundance of magic. Raw magic in its forms is unusable (see the planes and planars and deities sections), so the limiting factor in magic use is the skill of the wielders to focus it, else the effects would be totally chaotic.
If all the power was evenly divided, everyone would live in an area with too much magic, causing total chaos. Luckily, more than three quarters total of the magic power of the world is locked in the essence streams, thus making the other areas livable.
These essaence concentrations are mainly of two types:
The lesser are nodes that come from below to surface and are relatively low power, though the power of even a small node dwarfs that of any wizard.
The greater are streams that flow from one place to other. Navigation past the streams is practically impossible. Only the navigators and maybe some other individuals can bypass them, all others must go around. These streams split the world into small pieces and make long distance travel very hard.
Normal effects for entering a node, or approaching a stream include everything from polymorphing to increased or decreased abilities to death. Though those able to channel the chaotic magics can lessen the impact.
Some skillfull masters of magic can call upon these chaotic magics and channel them to themselves or away from themselves. Senior masters of the arcane academy are rumored to be among those.
Sometimes a region expreriences a high concentration of magic, these are called essence storms. Depending on the severity, there can range from strong strorms to changes of everything to total devastation of an area. These storms are most common close to the streams.
There are more than 800 known nodes and more than 200 known streams in the Western hemisphere.