Keyline design is a landscaping technique of maximizing the beneficial use of the water resources of a tract of land. The "keyline" denominates a specific topographic feature related to the natural flow of water on the tract. Keyline design is a system of principles and techniques of developing rural and urban landscapes to optimize use of their water resources. Australian farmer and engineer P. A. Yeomans invented and developed Keyline design in his books The Keyline Plan, The Challenge of Landscape, Water For Every Farm, and The City Forest.