The Public Land Survey System is the rectangular framework under which most land west of the original colonies was surveyed and disposed of. It is not a grid laid over existing parcels; it is the survey that created them. That distinction governs everything else, because a boundary established by an original government survey is where that survey put it, not where a perfect rectangle would have been.
For a technician the system matters in two ways. Descriptions arrive written in its language and have to be read correctly, and retracement depends on knowing what the original surveyors were instructed to do and what they actually did. The vocabulary is an afternoon's work; the evidence takes considerably longer.
Principal meridians and base lines
Each PLSS survey area is referenced to an initial point, through which a principal meridian was run north and south and a base line east and west. There are dozens across the country, each covering a region, and a description is ambiguous without naming the one it belongs to.
From that origin the land was divided into townships six miles square. A township is identified by how far it lies north or south of the base line and how far east or west of the principal meridian: T2N R3W means the second township north of the base line in the third range west of the principal meridian.
- Township
- Nominally a six-mile square containing thirty-six sections, and also the north-south coordinate in the township-and-range reference. The word does both jobs, so T2N is the tier number while the township is the block of land it identifies.
- Range
- The east-west coordinate of a township, counted east or west from the principal meridian. Ranges are columns of townships; townships in the tier sense are rows.
Sections and their numbering
Each township is divided into thirty-six sections, nominally one mile square and containing 640 acres. The numbering runs in a boustrophedon pattern: section 1 in the northeast corner, west along the north tier to section 6, down to section 7, east to section 12, down again, and so on, with section 36 ending in the southeast corner.
| Unit | Nominal size | Nominal area |
|---|---|---|
| Township | 6 miles square, 480 chains | 23,040 acres |
| Section | 1 mile square, 80 chains | 640 acres |
| Quarter section | 40 chains square | 160 acres |
| Quarter-quarter section | 20 chains square | 40 acres |
| Sixteenth of a quarter | 10 chains square | 10 acres |
Aliquot parts and how to read a description
Land within a section is described by repeated halving and quartering, called aliquot parts. The description reads from the smallest part outward, so each term qualifies the one after it.
The NE 1/4 of the SW 1/4 of Section 14, T2N R3W of a named principal meridian, means: take Section 14, take its southwest quarter, and within that take the northeast quarter. The result is nominally 40 acres. Read it right to left to locate the parcel, then left to right to state its size: each quartering divides the area by four, and each halving by two.
| Description | Nominal area | Reading |
|---|---|---|
| NE 1/4 | 160 acres | The northeast quarter of the section |
| NE 1/4 SW 1/4 | 40 acres | The northeast quarter of the southwest quarter |
| S 1/2 NE 1/4 | 80 acres | The south half of the northeast quarter |
| N 1/2 SE 1/4 NW 1/4 | 20 acres | The north half of the southeast quarter of the northwest quarter |
Every area in that table is nominal. An aliquot part is defined by geometry - by the corners the original survey set and the midpoints between them - not by acreage, so the deed conveys the part regardless of what it measures. Where a stated acreage conflicts with the aliquot call, the aliquot call ordinarily prevails.
Why sections are not 640 acres
Two things prevent the rectangular ideal. Meridians converge toward the pole, so ranges cannot stay six miles apart as they run north; and the surveys were run on the ground with chains, over rough country, with the accumulated error that implies.
Convergence was handled by resetting the framework periodically. Standard parallels, also called correction lines, were run east and west at intervals, and guide meridians north from them, so convergence accumulated only over a limited distance before the grid was re-established. Where a range line meets a standard parallel from the south it sets a closing corner, which generally does not coincide with the standard corner set from the north - the double corners that confuse people expecting a clean grid.
Excess and deficiency within a township were placed deliberately. The instructions put the irregular measure into the north and west tiers of sections so the interior sections could be regular. That is why fractional lots appear along the north and west edges of a township.
Government lots
Where a part of a section cannot be described as an aliquot part, it is numbered as a government lot. Lots arise in the north and west tiers where excess and deficiency were absorbed, and wherever a section is broken by a navigable water body, a reservation, an earlier grant or a state line.
Corners and the evidence they represent
The system is built on physical corners, and the corners rather than the geometry define the boundaries. The categories worth knowing are few.
- Section corners, at the intersections of section lines, and quarter corners at the midpoints of section lines. Together they frame every section and control the subdivision of it.
- Meander corners, set where a survey line meets a navigable water body, from which the meander line was run. The meander line describes the shoreline; it is generally not the boundary, which is the water itself.
- Witness corners, set on line at a measured distance from a true corner that could not be monumented where it fell - in a stream, on a cliff, in a road.
- Closing corners, set where a line closes onto a previously established line such as a standard parallel, as distinct from the standard corner set when that line was originally run.
The controlling principle in retracement is that an original corner, if its position can be established by acceptable evidence, is where the boundary is - whatever the measurements say. A lost corner, one whose position cannot be recovered from any evidence, is restored by proportionate measurement from the nearest existing corners. An obliterated corner, whose monument is gone but whose position can be established from testimony, marks, fences or records, is not lost and is not proportioned.
Subdividing a section
Quarter-quarter corners were not set by the original surveys. The interior of a section is subdivided by the retracing surveyor according to rules that are geometric rather than arithmetic: the center quarter corner lies at the intersection of the straight lines joining opposite quarter corners, not at the computed center of the section.
Where to go next
The authoritative source is the Bureau of Land Management Manual of Surveying Instructions, which is in the public domain and freely available. It governs retracement of PLSS boundaries on federal land, and it is far more readable than its length suggests.