Legal description glossary
The rectangular survey system locates land through a nested public grid
Start at the principal meridian and base line, find the township and range, select the section, then divide into the stated fractions.
Last updated: August 1, 2026
Rectangular survey system: definition first
Direct answer: The rectangular survey system, also called the government survey or Public Land Survey System, identifies land by reference to a principal meridian, base line, township, range, section, and smaller aliquot parts or government lots. A township is nominally six miles square and contains 36 sections. A section is nominally one square mile or 640 acres, but original surveys and correction methods can produce irregular dimensions and government lots.
Why it is on the exam: PSI lists the government survey, or rectangular survey, as a legal-description method in Property Ownership and separately tests land measurement. The BLM's current specifications describe the same nested grid, nominal areas, numbering plan, and use of aliquot parts.
Township size
Nominally 6 miles by 6 miles
Sections
36 per township
Section size
Nominally 640 acres
Quarter-quarter
Nominally 40 acres
Keep township direction and range direction on different axes
| Decision point | Township designation | Range designation |
|---|---|---|
| Reference line | Base line | Principal meridian |
| Direction | North or south | East or west |
| Example | Township 3 North | Range 2 West |
| Combined result | Horizontal tier position | Vertical range position; together they identify the township |
Build the address from the outside grid inward
The principal meridian runs north and south from an initial point. The base line runs east and west. Township lines create tiers north or south of the base line, and range lines identify columns east or west of the principal meridian. Their intersection locates a nominal six-mile-square township.
The principal meridian name matters because more than one survey region can contain a Township 3 North, Range 2 West. The meridian places that repeated township-range label in the correct survey system.
- Name the principal meridian.
- Move north or south from the base line for the township number.
- Move east or west from the meridian for the range number.
- Select the numbered section and then its smaller subdivision.
Number sections like an ox turning at each row
Section 1 begins in the township's northeast corner. The numbering runs west through section 6, drops south, returns east through section 12, and continues back and forth until section 36 in the southeast corner. The pattern is sometimes called boustrophedonic or remembered as the path of an ox plowing alternating rows.
Do not number every row from the same side. That would place sections 7 through 12 backward and break the official sequence. A quick six-column sketch is safer than relying on a vague picture under exam pressure.
Calculate aliquot acres by multiplying every fraction
Begin with the nominal 640-acre section. A half section is 320 acres. A quarter section is 160 acres. A quarter of a quarter is 40 acres. The north half of the southwest quarter is 640 multiplied by one-quarter and then one-half, or 80 nominal acres.
Aliquot parts are proportional subdivisions, while government lots can be irregular. Curvature of the earth, convergence of meridians, original survey conditions, and correction practices mean the words one mile and 640 acres are nominal. The original survey corners, plats, field notes, and governing rules control the real parcel.
Calculate before reaching for the section map
Question: A description conveys the east half of the northwest quarter of a nominal section. How many acres does the exam calculation produce before considering survey irregularities?
Best answer: 80 acres.
Why: Start with 640 acres, multiply by one-quarter for the northwest quarter to get 160, then multiply by one-half for the east half to get 80. The location and acreage operations are separate tasks.
Lock in the distinction
Exam trap
Do not say every section contains exactly 640 acres. The BLM describes sections and townships as nominal sizes, and correction areas or government lots can be irregular.
Memory cue
Meridian and base line, township and range, section and share. Multiply every share by 640.
Quick questions
How many sections are in a township?
A standard rectangular-survey township contains 36 sections arranged in a nominal six-mile-square grid.
How many acres are in a section?
A section is nominally 640 acres. Original survey and correction conditions can produce irregular actual acreage.
Where is section 1?
Section 1 is in the northeast corner of the township. Numbering then moves west and alternates direction in each row to section 36 in the southeast.
How many acres are in a quarter-quarter section?
Nominally 40 acres: 640 multiplied by one-quarter and one-quarter.
Primary sources and review status
- PSI Illinois Real Estate Candidate Information Bulletin, June 24, 2026
- U.S. Bureau of Land Management, Specifications for Descriptions of Land, revised 2017
- U.S. Bureau of Land Management, Manual of Surveying Instructions
Checked through August 1, 2026. This definition is an exam-prep explanation, not a substitute for current law or advice about a live dispute. The current official source controls if the outline or Illinois rule changes.