Eliode: The Strophean Chronicle
Magical effects are powered by the flow of Mana. Different schools of magic access and manipulate this mana in different ways but all magical spells are powered by Mana.
Devine effects do not use mana, instead the gods simply change the world to better suit their mood.
Spell Casters must channel and manipulate mana to achieve the ends they seek. Limitations in the availability of mana restrict the size and power of any particular spell.
Mana flows slowly through the world. Paths of Mana form between large magical effects, enchantments, artifacts, sites of rituals or large magical battles. These paths are known as Ley Lines. As an example enchantments slowly fade giving up the Mana used, this mana then flows away through Ley Lines. The flow of this mana tends to move toward areas where there is need for the magic, while the nuances are a little complicated there are some major Ley Lines that seem permanent. Other minor lines fluctuate and change regularly.
Differing schools of magic use mana in different ways, some draw it to the spell caster, some use the mana stored in their own bodies, some effect the mana stored in objects and people around them
Most schools can detect mana as it is used or manipulated.
One sub-branch of wizardry and a large number of druidic mages make a specific study of how mana moves and how ley lines form.