A township in the United States is a small geographic area. Townships range in size from 6 to 54 square miles (15.6 km² to 140.4 km²), with 36 square miles (93 km²) being the norm.
The term is used in three ways.
#A survey township is simply a geographic reference used to define property location for deeds and grants as surveyed and platted by the General Land Office (GLO). A survey township is nominally six by six miles square, or 23,040 acres.
#A civil township is a unit of local government. Civil townships are generally given a name, sometimes abbreviated "Twp".
#A charter township is similar to a civil township, found only in the state of Michigan. Provided certain conditions are met, a charter township is mostly exempt from annexation from contiguous cities or villages, and carries additional rights and responsibilities of home rule.
(詳細はPublic Land Survey System (PLSS). A reference to the township will look something like "Township 2 North Range 3 East", or "T2NR3E" and such a notation is used in property descriptions based on the PLSS. Townships were originally surveyed and platted by the United States General Land Office, using contracted private survey crews, and are marked on the United States Geological Survey maps of the United States.
Townships are normally a square approximately on a side with cardinal boundaries conforming to meridians and parallels, containing 36 sections of each. The northern and western most tier of sections in each township are designed to take up the convergence of the east and west township boundary lines or range lines, as well as any error in the survey measurements, and therefore these sections vary slightly from being one square mile or . Survey townships exist in some form in most states other than the original 13 colonies, Kentucky, Tennessee, Vermont, and Maine. Irregular or fractional townships with fewer than a full 36 sections are created where full townships cannot be laid out due to existing senior boundaries, such as Spanish/Mexican ranchos, Indian reservations, state boundary lines, etc.
This kind of township is similar to geographic townships in the province of Ontario, Canada.
In Kentucky, the Jackson Purchase (the area west of the Tennessee River) is divided into townships and ranges. In Tennessee, the entire state is surveyed into townships and ranges that make up 13 survey districts of the Tennessee State Survey. In extreme northern Maine there is an area divided into townships and ranges oriented to true north. A region in the central part of the state, made up of 17 surveys, is divided into townships, but these are not oriented to true north. The remainder of the state is on metes and bounds. Similarly, Vermont and New Hampshire are mostly metes-and-bounds states, but have areas in the north that are surveyed into townships not oriented to true north. Most of Ohio is surveyed using the Public Land Survey System, but several sizable areas are metes-and-bounds, including the Virginia Military Reserve, Donation Tract, French Grant and the three Moravian grants (Gnadenhutten, Schoenbrunn and Salem). A area in southern Indiana (Clark Grant) is not surveyed into townships, but is still a gridded survey. Portions of the Texas State Survey use square townships. Sizeable portions of Alaska, Washington, Oregon, California and Arizona are unsurveyed. Substantial swampy areas in Florida and Louisiana are also unsurveyed.
Both New York and Pennsylvania have metes-and-bounds surveys, but in the western parts of these states, the metes-and-bounds form square townships many of which are also civil townships. Besides these, nearly every state has areas of metes-and-bounds that were never included in the grids (like along major rivers) or were removed from the grid, usually due to surveying mistakes.
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