<Li> Township (Twp, T): (1) Synonym for survey township, i.e., a square parcel of land of 36 square miles, or (2) A measure of the distance north or south from a referenced baseline, in units of six miles . </Li> <Li> Witness: Any marker set on the ground that marks or represents some other, nearby object or location of surveying importance, such as a corner . A bearing tree is a witness to a survey corner . </Li> <P> The surveying of any regional area, such as a state or two, is a multi-step process . First, two controlling survey lines are established: a baseline, which runs east - west and a principal meridian, which runs north - south (Fig. 1). The locations of the two are determined by a previously chosen initial point, where they originate and thus intersect . Next, at a defined distance interval, commonly 24 or 30 miles (48 km) depending on the year and location, standard parallels of latitude are established parallel to the baseline . The meridian, baseline and standard parallels thus established form a lattice upon which all further surveying is then based . Subsequent work divides the land into survey townships of roughly 36 square miles (~ 93 km) or 6 miles (~ 9.7 km) on each side . This is done by the establishment of township and range lines . Township lines run parallel to the baseline (east - west), while range lines are true meridians and thus run north - south; each are established at six mile (10 km) intervals . Lastly, townships are subdivided into 36 sections of approximately one square mile (640 acres, ~ 2.6 km) and sections into four quarter - sections of 0.25 square mile (160 acres, ~ 0.65 km) each . (See descriptions and figures illustrating the system). The intersection of a township line (or baseline) with a range line (or principal meridian) constitutes a township corner, of a section line with any other type of line a section corner, and a point halfway between any two section corners a quarter corner . The federal government typically surveyed only to this quarter - section level, the subdivision of smaller parcels being carried out subsequently by private surveyors after original sale . </P> <P> Because the survey design is two - dimensional (rectangular), while the actual earth is three - dimensional (~ spherical), adjustments to land areas must be made periodically to prevent error propagation; not all sections can be one square mile nor can all townships be exactly 36 square miles . More specifically, all north - south running lines (all range lines and half of all section lines), as with the prime meridian, are always established with reference to true, geodetic north . But it is a physical impossibility to meet this condition and still maintain a rectangular land grid, because such lines converge on the north pole--they are meridians . </P>

East-west lines in the government rectangular survey system are known as