These are tile Improvements that allow Civilizations to utilize Magic from the Speres of the Mana node created. Such as an Air Node will allow Air I, Air II, and Air III promotions to be learned by your civilization units. It is advantageous to have many Mana Nodes of the Same Node. Example. 1 Air Node - Access to Air Sphere. 2 Air Nodes - Acess to Sphere, and Free Air I promotion to your Units. 3 Air Nodes - Acess to Sphere and Free Air I and Air II promotion to your Units. 4 Air Nodes - Acess to Sphere and Free Air I, Air II, and Air III promotion to your Units.