Survey township, sometimes called Congressional township, as used by the United States Public Land Survey System, refers to a square unit of land, that is nominally six (U.S. Survey) miles (~9.7 km) on a side. Each 36 square mile (~93 km²) township is divided into 36 one-square mile (~2.6 km²) sections, that can be further subdivided for sale, and each section covers exactly 640 acres.