Sanctum invocation

A Sanctum Invocation is a ritual spell that binds a wizard to an area of land that has some sort of sentient or sapient properties, known as a genius loci.

Description
Most commonly the bond gives power to the wizard but it is known to give other abilities like intellectus if the Genius Loci in question has great age or power. The abilities granted by the bond are unable to have an effect outside the area they control. It is theoretically possible to have such an effect but highly unlikely considering that one with intellectus confined to its territory is considered extremely unusual.

Turn Coat
Harry Dresden used the Sanctum Invocation to claim the uncharted island in Lake Michigan. The process involved Harry summoning the island's spirit up by casting a ritual spell augmented with Soulfire. Harry then had to fight the spirit using the four classical elements. It was at this time that he named the spirit Demonreach. After physically connecting himself with the island by standing upon it he is able to "know" things occurring on the island that he wouldn't be able to know normally (i.e., locations of snakes, bees, people, etc). According to Harry, "I punched it in the nose. Now we're friends." Harry is expressly warned by the Gatekeeper against drawing on the island's power as he does not have the skill to control it yet.