Public Land Survey System

Principal Meridians and Base Lines
  Counties, Townships and Ranges Explained

  Example and Explaination
  Meridians and Base Lines of Illinois

History of the Public Land Survey System
  The rectangular survey system was enacted by the Land Ordinance Act of 1785.  Now known as the Public Land Survey System, this system divided the western lands into grid-shaped townships and sections.  Surveyed land was sold by the government, providing important revenue for the cash-starved nation. Previous to the Public Land Survey System, land was surveyed using a confusing landmark-based system called metes and bounds.
  The Public Land Survey System is coordinate-based, with all distances and bearings made from north-south running meridians and east-west base lines.  The largest subdivision of land is the Public Land Survey Township (as opposed to political township), and measures six miles square.  Each township is comprised of 36 sections, and each section has an area of one square mile (640 acres).

Office of U.S. Surveyor General
  The office of U.S. Surveyor General was created in 1796 to survey lands as the nation expanded westward.  In 1836 the office was placed under the jurisdiction of the General Land Office (GLO).  In 1849, the GLO was moved under the Department of Interior.  The office of Surveyor General was closed in 1925, and surveying responsibilities remained with the GLO.  In 1946, the GLO was abolished, and surveying duties transferred to The Bureau of Land Management (BLM).

How the Plats Were Created
  The survey progressed continuously in some areas and discontinuously in others.  The surveyor general and the commissioner of the GLO decided which tracts were to be surveyed in a given fiscal year.  Preference was often given to lands that had commercial value and could be sold immediately.  The ongoing settlement of Indian lands also affected the process.  Often reservation lands were not surveyed until significantly later.

In The Field
  Contracts for survey work were awarded to deputy surveyors by competitive bid.  The deputy surveyor, with a crew of chainmen, axemen, and a compassman, ran the survey lines in the field and was responsible for erecting survey monuments, marking "bearing trees," and recording all measurements in his field notes.  The deputy surveyor's work was verified by the surveyor general, and the field notes and plats submitted to the commissioner of the GLO for approval.
  Distances were measured using chains and links.  Chains measured 66 feet long, with 80 chains equaling one mile.  Each chain was made up of 100 links of 7.92 inches each.  Alignment was determined using a compass or a solar compass.  In areas where measuring by chains was not possible, such as lakes or hilly terrain, distances were calculated using triangulation.
  To demarcate the boundaries of townships and sections, surveyors usually placed monuments - typically wooden posts - at township and section corners, and at quarter-section corners.  To insure these corners could be found if the posts were destroyed, surveyors marked "bearing trees" nearby the posts.  In prairie areas, they built earth mounds around the posts, about three feet high.
  When a corner fell in a body of water, a "meander corner" was established, and the true corner then ascertained by triangulation or direct measurement.  Meander corners marked the intersection of section lines and a water body.  A "witness corner" was used to designate a section or quarter corner when the corner was located where monumentation was impractical.
  The deputy surveyor was also responsible for mapping the physical geography of surveyed lands.  Plats show lakes, rivers, swamps, waterfalls, and areas of prairie and forest, and other features.  In areas with navigable watercourses or sizeable lakes, plats sometimes include surveys of bank meanders.  Also occasionally noted are man-made features such as settlements and roads.  The deputy surveyor's field notes include more detailed information, such as soil type, vegetation, and mineral deposits.

Public Land Survey System Explained

The Public Land Survey System is a coordinate-based system that organizes land into a strict grid pattern.  Public Land Survey Townships (as opposed to political townships) form the basic unit of land division, and measure six miles square.  Each township is comprised of 36 sections, and each section has an area of one square mile (640 acres).

Public Land Survey Townships are named systematically by the township and range numbering system.  This system is based on the location of an initial point.  Initial points occur at the intersection of a principal meridian and a base line.  Each township is named by a township number, which indicates its north-south position of the base line, and a range number, which indicates its east-west position of the principal meridian.

Public Land Survey Townships are subdivided into 36 sections, each section being approximately 1 mile by 1 mile in dimension. Section corners and section-quarter corners were marked by posts or other monuments.  Sections are numbered from 1 to 36 and are labeled in a switchback pattern.

Each section can be divided into four quarters: NW, NE, SW, and SE.  Each quarter is 160 acres, and these areas too can be subdivided into NW, NE, SW, and SE quarters.

For land located at T43N R20W S6 SW1/4:
  Township = 43 North of the Base Line, Range = 20 West of the Principal Meridian, Section = 6, and the land constitutes the section's southwest quarter.

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