As a Public Domain state, Arizona uses a rectangular surveying system called the Public Land Survey System (PLSS). It was originally set forth by an ordinance passed by the Continental Congress in 1785. The ordinance provides for a rectangular grid of townships that are approximately 6 miles square. Each township is further subdivided into 36 sections, each approximately 1 mile square. As a result of convergence of meridians and errors in field work, the boundaries of townships and sections are not exact. The original Arizona cadastral survey "plats" were done by what was then called the General Land Office (GLO) in the late 1800's and early 1900's. General Land Office Survey Maps show those original maps for the entire state of Arizona.
The approximately 27 square mile Canoa Land Grant area was not included in the original survey and is not part of the of the Public Land Survey System. The original General Land Office Survey Maps clearly show the exclusion of the Canoa Land Grant in Township 18 Range 13 East, Township 18 Range 14 East, and Townshp 19 Range 13 East. You can also see the Canoa Land Grant as the long, angled rectanglular area in the southern Pima County border in the eastern part of the county in the township numbering map below. Even though the survey did not survey or define sections in the Canoa Land Grant area our Pima County GIS system shows sections in the Canoa Land Grant area as they might have been had the Canoa Land Grant area been part of the survey. These fictitious Canoa Land Grant area "sections" enable us to store and manage GIS data throughout Pima County in a consistent manner.
Townships are located and numbered starting from a reference point defined by a baseline and a principal meridian identified for each survey district. There are two survey districts in Arizona: the Gila and Salt River, and Navajo. The Navajo survey district is relatively small comprising the northeast corner of Arizona and the northwest corner of New Mexico. Most of Arizona, including Pima County, makes up the Gila and Salt River survey district.