Ley Lines, the Manasphere
There exists a magical analog of the tectonic plate system (core,
mantle, crust) on Jovia. Like our own planet's (geological) temperature
gradient, Jovia's mana intensity decreases as the distance from
the world's core increases. The surface of the magical "crust"
of Jovia's manasphere lies about 15 miles above the planet's physical
crust, hence the (mostly) world-wide normal mana level.
Ley lines are divergent boundaries in the planet's manasphere. Like
geological divergent boundaries allow hot magma to flow out of the
crust, ley lines allow raw magical energy to radiate into space.
The intensity of this flow is tempered by the presence of living
matter, which is itself mildly magical.
Note that the geological metaphor for Jovia's manasphere, while
apt for most discussions, is not entirely accurate. Mana (raw magical
energy) behaves unlike any physical substance. But treating it as
a gas or liquid is usually easier for the purposes of visualization.
Ley Line, Node, and Locus Effects
So what are the effects of ley lines on magical activity? Ley
lines raise the mana level to "high" in their immediate
area (anywhere from 18" to 25' in width). In fact, ley lines
might be more accurately referred to as "ley planes"
since they extend very far up and down and forward to back. Their
smallest dimension is width.
Ley line intersections are special. The intersection of two lines
is called a "ley node." While the mana level at a ley
node is unaffected, magic is easier to use and the area affected
is larger (forming a circle/cylinder with a radius of 5 to 60 times
the width of the widest ley line). All magic users (even those without
Magery) get a +2 to their effective skill with any spell they attempt
to cast within the area of the intersection.
The intersection of three lines at a single point is called a "ley
locus." These points form a circle with a diameter double the
width of the widest line. Here, the mana level is "very high,"
magic users get a +4 to skill, enchantment costs 50% less, and the
Magery level of any person is raised by one. These are, of course,
Powerful enchantments (i.e. with an energy cost of 800 or more)
act as a conductor for raw magical energy and give it the means
to transform into other, dangerous forms of energy. Mana-arcs behave
like electric bolts, except they "ground" into zones of
lower mana or less powerful enchantments. In game terms, mana-arcs
do burning damage (anywhere from 1d to 6dx10). Dampening enchantments
designed to insulate specific artifacts do exist, but the energy
cost is often prohibitive (about 30% of the total energy invested
in the object). Most people find it easier to either temporarily
dampen an artifact with a spell, ground it into a normal mana zone
(usually via a silk rope enchanted with Manastone), or keep the
artifact in a specially enchanted container.
Ley Line-Dependant Enchantments
Some enchantments can be made to only work on ley lines for
a reduction in total energy cost. The Power enchantment is notably
cheaper when modified to allow the item to draw energy from a line.
These "discounts" make line-dependant flying ships feasible.