Map dowsing is done to discover points along geographical lines of energy. In an article for SERI (Subtle Energy Research Institute)Worldwide, Geoffrey Pearl-Tang describes dowsing with a thin cotton string and pendulum to map out a significant framework of subtle energy. He holds the pendulum in one hand and a pencil in the other while drawing small crosses on a map in points where the pendulum shows a point of along thee energy body. Soon a line forms around a structure of energy. Read more at SERI-Worldwide’s Map Dowsing by Geoffrey Pearl-Tang.