A survey township, sometimes called a Congressional township or just township, as used by the United States Public Land Survey System, is a nominally-square area of land that is nominally six U.S. survey miles (about 9.66 km) on a side. Each 36-square-mile (about 93.2 km2) township is divided into 36 sections of one square mile (640 acres, roughly 2.6 km2) each. The sections can be further subdivided for sale.
The townships are referenced by a numbering system that locates the township in relation to a principal meridian (north-south) and a base line (east-west). For example, Township 2 North, Range 4 East is the 4th township east of the principal meridian and the 2nd township north of the base line. Township (exterior) lines were originally surveyed and platted by the US General Land Office using contracted private survey crews. Later survey crews subdivided the townships into section (interior) lines. Virtually all lands covered by this system were sold according to those boundaries and are marked on the U.S. Geological Survey topographic maps.