PLSS, Recorded Plats, and Area Calculations

PLSS, Recorded Plats, and Area Calculations

2. Government Rectangular Survey System (PLSS)

The Public Land Survey System (PLSS), commonly referred to as the Government Rectangular Survey System, was established by the Continental Congress under the Land Ordinance of 1785. Designed under the leadership of Thomas Jefferson, it created a standardized, grid-based land identification framework for public domain lands ceded to the federal government. Today, the PLSS covers 30 public land states spanning the Midwest, the South (Alabama, Mississippi, Florida, Louisiana, Arkansas), the Great Plains, and the entire American West.

Grid Architecture: Principal Meridians and Base Lines

The PLSS is organized around intersection points established astronomically by federal surveyors:

• Principal Meridian: A true north-south line of longitude running through an established Initial Point. There are 37 named Principal Meridians across the United States (e.g., the 6th Principal Meridian, the Willamette Meridian, the San Bernardino Meridian).
• Base Line: A true east-west line of latitude intersecting the Principal Meridian at the Initial Point.
• Standard Parallels (Correction Lines): East-west lines surveyed parallel to the Base Line at 24-mile intervals north and south to compensate for the curvature of the Earth.
• Guide Meridians: North-south lines surveyed at 24-mile intervals east and west of the Principal Meridian.

Townships and Ranges

The grid creates 6-mile-wide horizontal tiers and vertical columns:

• Township Tiers: Strips of land 6 miles wide running east-west, numbered consecutively North or South of the Base Line (e.g., Township 1 North, Township 2 North, Township 1 South).
• Range Lines: Strips of land 6 miles wide running north-south, numbered consecutively East or West of the Principal Meridian (e.g., Range 1 East, Range 2 East, Range 1 West).
• Township (Congressional Township): The 6-mile by 6-mile square formed by the intersection of a township tier and a range line. A standard township covers 36 square miles and contains 23,040 acres ($36 \times 640 = 23,040$).

Section Architecture and Boustrophedon Numbering

Each 36-square-mile township is divided into 36 sections. A nominal regular section is described as measuring:

• 1 mile by 1 mile (linear boundaries)
• 5,280 feet by 5,280 feet
• 1 square mile in area
• 640 acres ($5,280 \times 5,280 = 27,878,400\ \text{sq ft}$; $27,878,400 \div 43,560 = 640\ \text{acres}$)

Sections are numbered 1 through 36 in a distinct serpentine order known as boustrophedon (meaning "as the ox plows"). Numbering starts in the northeast corner with Section 1, proceeds west to Section 6, drops south to Section 7, proceeds east to Section 12, drops south to Section 13, and alternates back and forth down to Section 36 in the southeast corner.

+-----+-----+-----+-----+-----+-----+
|  6  |  5  |  4  |  3  |  2  |  1  |  <-- Proceeds West (1 to 6)
+-----+-----+-----+-----+-----+-----+
|  7  |  8  |  9  | 10  | 11  | 12  |  --> Proceeds East (7 to 12)
+-----+-----+-----+-----+-----+-----+
| 18  | 17  | 16  | 15  | 14  | 13  |  <-- Proceeds West (13 to 18)
+-----+-----+-----+-----+-----+-----+
| 19  | 20  | 21  | 22  | 23  | 24  |  --> Proceeds East (19 to 24)
+-----+-----+-----+-----+-----+-----+
| 30  | 29  | 28  | 27  | 26  | 25  |  <-- Proceeds West (25 to 30)
+-----+-----+-----+-----+-----+-----+
| 31  | 32  | 33  | 34  | 35  | 36  |  --> Proceeds East (31 to 36)
+-----+-----+-----+-----+-----+-----+

Section 16 was traditionally reserved by the federal government for the support of public schools in each township.

Fractional Sections and Government Lots

Because the Earth is a sphere, lines of longitude converge as they travel north toward the North Pole. A township's northern boundary is physically narrower than its southern boundary. Federal survey instructions dictate that this curvature convergence (roughly 24 to 30 feet per township tier), along with accumulated field measurement errors, must be absorbed entirely into the north and west boundaries of the township.

Irregularities are commonly accommodated along northern and western township boundaries. Do not assume that every named section has a particular deficiency or that all other sections contain exactly 640 acres; the official survey plat and government-lot acreage control. Within these fractional sections, non-standard parcels or parcels bordering navigable water bodies that cannot be described as regular quarter-quarters are assigned specific parcel numbers known as Government Lots (e.g., "Government Lot 3 of Section 6").

Calculating Aliquot Part Acreage

Standard sections are subdivided into fractional subdivisions known as aliquot parts. A section of 640 acres can be quartered into four 160-acre quarter-sections ($NW\ \frac{1}{4}$, $NE\ \frac{1}{4}$, $SW\ \frac{1}{4}$, $SE\ \frac{1}{4}$). Each quarter section can be further divided into quarter-quarters (40 acres), and half-quarter-quarters (20 acres).

To calculate the acreage of an aliquot legal description, follow this standard procedure:

1. Begin with the standard section acreage of 640 acres.
2. Identify all fraction denominators in the description.
3. Divide 640 sequentially by each denominator (reading either left-to-right or right-to-left, because the calculation multiplies the starting area by each reciprocal factor; division itself is not associative).

$\text{Acreage} = 640 \div d_1 \div d_2 \div d_3 \dots$

Worked Calculation 1: Standard Aliquot Part

Calculate the acreage of the $N\ \frac{1}{2}$ of the $SE\ \frac{1}{4}$ of the $SW\ \frac{1}{4}$ of Section 24, T2N, R4W.

• Denominators present: 2, 4, 4
• Step 1: $640 \div 2 = 320\ \text{acres}$
• Step 2: $320 \div 4 = 80\ \text{acres}$
• Step 3: $80 \div 4 = 20\ \text{acres}$
• Alternative Multiplicative Method: $\frac{1}{2} \times \frac{1}{4} \times \frac{1}{4} = \frac{1}{32}$; $640 \times \frac{1}{32} = 20\ \text{acres}$.

Worked Calculation 2: Compound Parcel with "AND"

Calculate the acreage of the $S\ \frac{1}{2}$ of the $NE\ \frac{1}{4}$ AND the $NE\ \frac{1}{4}$ of the $NW\ \frac{1}{4}$ of Section 12, T4S, R1E.

• Tract 1: $S\ \frac{1}{2}$ of the $NE\ \frac{1}{4}$
  • Denominators: 2, 4
  • Calculation: $640 \div 2 \div 4 = 80\ \text{acres}$
• Tract 2: $NE\ \frac{1}{4}$ of the $NW\ \frac{1}{4}$
  • Denominators: 4, 4
  • Calculation: $640 \div 4 \div 4 = 40\ \text{acres}$
• Total Tract Acreage: $80 + 40 = 120\ \text{acres}$

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3. Lot and Block System (Recorded Plat)

The Lot and Block system (also referred to as the Recorded Plat system or Recorded Map system) is the predominant legal description framework used for urban and suburban residential properties across the United States.

The Subdivision Plat Recording Process

When a large rural or raw tract of land (originally described by metes and bounds or PLSS aliquot parts) is designated for residential subdivision development, the developer follows a statutory platting process:

1. Boundary and Engineering Survey: A licensed professional land surveyor conducts a precision perimeter survey and drafts a detailed subdivision plat map.
2. Subdivision Engineering: The plat delineates individual building lots, blocks, dedicated public street rights-of-way, sidewalks, utility and drainage easements, building setback envelopes, parks, and stormwater retention basins.
3. Municipal Regulatory Review: The plat map is submitted to the local planning commission, zoning board, and municipal engineering authority for formal review and approval, verifying compliance with subdivision regulations, utility connectivity, and street design standards.
4. Public Recordation: Upon approval, the final plat is officially filed and recorded in the county land records (office of the county recorder, register of deeds, or clerk of court). The plat is assigned an official book and page number or document instrument number (e.g., Plat Book 48, Pages 12 through 15).

Format of a Lot and Block Legal Description

Once recorded, every individual lot on the plat map has a complete, self-contained legal description that incorporates the recorded plat by reference:

"Lot 14, Block B, Whispering Pines Subdivision Phase II, according to the map or plat thereof recorded in Plat Book 32, Pages 44-46, in the Public Records of Orange County, Florida."

This concise description is legally sufficient because it incorporates every line, angle, distance, setback, and easement drawn on the official recorded plat map.

Assessor's Parcel Number (APN) vs. Formal Legal Description

An Assessor's Parcel Number (APN)—also known as a Tax Parcel Identification Number (PIN), Tax Folio Number, or Parcel ID—is a numeric or alphanumeric identifier assigned by the local county tax assessor for the sole purpose of ad valorem property tax administration (e.g., APN: 042-181-009-00).

Appraisers must never substitute a bare APN for the formal legal description in an appraisal report. The appraiser must obtain and review the recorded deed or recorded subdivision plat to verify that the legal description matches the physical property boundaries inspected in the field.

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Comparison of the Three Primary Land Survey Systems