PS Exam Preparation

Comprehensive preparation for the NCEES Principles and Practice of Surveying (PS) exam. 5 modules covering all 5 exam domains with 50 in-depth topics.

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Lesson 1

BLM Manual of Surveying Instructions

Learning Objectives

After completing this topic, you should be able to:

Distinguish between original surveys and dependent resurveys
Identify the four categories of PLSS corners and their restoration rules
Apply single and double proportionate measurement methods
Explain the legal authority and purpose of the BLM Manual
Describe the procedures for subdividing sections
Understand when an independent resurvey is appropriate vs. a dependent resurvey

Overview

The Bureau of Land Management (BLM) Manual of Surveying Instructions (2009 edition) is the authoritative reference governing the survey and resurvey of public lands in the United States under the Public Land Survey System (PLSS). While originally published to guide federal cadastral surveyors, its principles have been adopted by courts and practitioners nationwide as the standard for restoring PLSS corners and interpreting the rectangular survey system.

For the PS exam, this is where PLSS theory meets practice. You must understand the hierarchy of corner evidence, the difference between original and dependent resurveys, and the proportionate measurement methods used to restore lost corners.

Key Concepts

Authority and Purpose of the BLM Manual

The BLM Manual derives its authority from federal statutes governing the disposal and survey of public domain lands. The manual serves three primary purposes:

Establishing procedures for the original survey of unsurveyed federal lands
Defining methods for the resurvey and restoration of previously surveyed lands
Providing guidance for the subdivision of sections into aliquot parts

The manual is not a law itself, but it carries the weight of regulatory authority for federal surveys. State courts have widely adopted its principles for interpreting PLSS boundaries even on private land.

Figure PS.3.7 — BLM authority for the 2009 Manual of Surveying Instructions

Original Surveys vs. Resurveys

This distinction is fundamental to the PS exam.

Original Survey: The first official government survey of a township. An original survey creates boundaries -- it is a creative act. The monuments set, distances measured, and plat filed in the original survey establish the legal boundaries of sections and townships. Even if measurements were inaccurate, the original survey controls because it was the act that created the property.

Dependent Resurvey: A resurvey that reestablishes the original survey boundaries based on all available evidence of the original corner positions. A dependent resurvey follows the footsteps of the original surveyor and restores corners to their original positions (or as close as evidence allows). It does not create new boundaries.

Independent Resurvey: A completely new survey that supersedes the original survey. Independent resurveys are rare and require specific Congressional authorization because they can alter property boundaries. They are used only when the original survey is so defective that restoration is impossible.

Feature	Original Survey	Dependent Resurvey	Independent Resurvey
Purpose	Create new boundaries	Restore original boundaries	Replace original survey
Authority	BLM directive	BLM directive	Congressional authorization
Effect on boundaries	Establishes them	Reestablishes them	May alter them
Frequency	Historical (mostly complete)	Common	Rare

Corner Categories

The BLM Manual classifies corners into four categories based on the quality of evidence available. The classification determines the restoration procedure.

Existent Corner: A corner whose position can be identified by verifying the evidence of the monument or its accessories (bearing trees, pits, mounds) as described in the original field notes. An existent corner is the best evidence and is accepted without question.

Obliterated Corner: A corner at whose point there are no remaining traces of the original monument or its accessories, but whose position can be recovered beyond reasonable doubt by the testimony of witnesses or by some acceptable evidence (written or physical). The key distinction: the position is known, but the physical monument is gone.

Lost Corner: A corner whose position cannot be determined beyond reasonable doubt, either from traces of the original marks or from acceptable evidence. A lost corner has no recoverable physical evidence and no reliable testimony. Lost corners must be restored by proportionate measurement.

Closing Corner: A corner established where a survey line intersects a previously established boundary. Closing corners are set at the actual point of intersection. They are not subject to proportionate measurement because their position is defined by the intersection itself.

Corner Type	Monument Present?	Position Known?	Restoration Method
Existent	Yes (or accessories)	Yes	Accept as found
Obliterated	No	Yes (from evidence)	Restore from evidence
Lost	No	No	Proportionate measurement
Closing	Varies	Defined by intersection	Not proportioned

Figure PS.3.1 — Single and Double Proportionate Measurement

Proportionate Measurement

Proportionate measurement is the BLM-prescribed method for restoring lost corners. The principle is that any error in the original survey is distributed proportionally among all intervals along the line. This ensures that no single property owner bears the entire burden of original survey error.

Single Proportion: Used when the lost corner lies on a line between two existent or recovered corners. The lost corner is placed at a position that gives the same proportional distance between the controlling corners as shown on the original plat.

For example, if the original plat shows four quarter-mile intervals along a section line but the total remeasured distance is 5,310 feet instead of 5,280 feet, each interval is proportionally adjusted to absorb its share of the 30-foot excess.

Double Proportion: Used when the lost corner is a standard township or section corner that lies at the intersection of two survey lines. The position is determined by proportioning along both the meridional (north-south) and latitudinal (east-west) lines independently, then combining the results to establish a single position.

Double proportion applies to:

Interior section corners (controlled by lines in two directions)
Quarter-section corners on lines that control in both directions

Single proportion applies to:

Quarter-section corners on established lines
Standard corners on a single line
Any corner controlled in only one direction

Key Rule: Proportionate measurement is used ONLY for lost corners. If any acceptable evidence exists to recover the corner position, proportionate measurement is not appropriate -- the corner is obliterated, not lost.

Common wrong path — proportioning an obliterated corner. The fastest way to generate a wrong answer on a PS PLSS question is to blur the line between lost and obliterated. If local residents remember where the stone was, or a bearing tree stump survives in the field notes' bearing and distance, the corner is obliterated — you recover its position from that evidence, not from proportioning. Proportioning is a last resort, used only when no recoverable evidence exists. Exam questions plant the trap by describing an "old iron post that was removed" or "plowed-under stone whose position the landowner still knows" — in those scenarios, the corner is obliterated and must be restored from evidence, not by splitting excess/deficiency across the interval. The BLM Manual is explicit: if acceptable evidence exists, proportionate measurement is inappropriate.

Quick retrieval check — try before reading on.

▶A section line runs 1 mile between existent section corners. The quarter-section corner at the midpoint is lost. The original plat records the line as 80.00 chains (5,280.00 ft). Your remeasurement between the existent end corners shows 5,295.00 ft. Where does the lost quarter corner go?

Single proportion applies (lost corner on a line controlled by two existent corners). The quarter corner's record position is at 40.00 chains (2,640.00 ft) from the south existent corner, which is exactly half the record distance. Placed proportionally in the measured distance: 2,647.50 ft from the south existent corner — exactly half of the 5,295 ft measured distance. The 15-ft excess is split evenly between the two half-mile intervals (7.5 ft each). This is the simplest single-proportion case: two existent corners, one lost corner at the known record proportion of the interval.

Subdivision of Sections

The BLM Manual prescribes specific methods for subdividing sections into aliquot parts (halves, quarters, quarter-quarters).

Standard Section (Interior Section):

Quarter-section corners are at the midpoints of section boundaries
The center of the section is at the intersection of lines connecting opposite quarter-section corners
Quarter-quarter corners are at the midpoints of quarter-section boundaries

Sections Along the North and West Boundaries of a Township: These sections absorb all excess or deficiency from the original survey. The north and west tiers of lots are fractional. When subdividing:

Standard quarter-section corners are placed at 40 chains from the south and east section corners
All excess or deficiency falls in the north and west half-mile
Fractional lots are created along the north and west boundaries

Irregular Sections: Sections with meandered water boundaries, mineral claims, or other irregular features require special subdivision procedures described in the manual.

Order of Procedure for Dependent Resurvey

The BLM Manual prescribes a systematic approach:

Research: Examine original field notes, plats, and all subsequent survey records
Identify existent corners: Begin with corners that can be positively identified
Recover obliterated corners: Use testimony, written records, and physical evidence
Restore lost corners: Apply proportionate measurement only after exhausting all evidence
Subdivide sections: Follow prescribed methods for creating aliquot part boundaries
Monument and record: Set durable monuments and prepare complete records

Figure PS.3.8 — Five-step BLM resurvey procedure

Evidence Evaluation for Corner Recovery

The BLM Manual establishes a hierarchy for evaluating corner evidence:

Original monument in place -- highest priority
Bearing trees or other accessories as described in field notes
Witness testimony from reliable sources who observed the original monument
Fence lines, occupation lines, and improvements that relate to the original corner
Proportionate measurement -- last resort for truly lost corners

The surveyor must exercise professional judgment in evaluating evidence. A single bearing tree that matches the original field notes (species, bearing, distance) is compelling evidence. Multiple lines of evidence pointing to the same location provide high confidence.

Exam Tips

The PS exam frequently tests the distinction between lost and obliterated corners -- remember that the difference is whether the position can be recovered, not whether the monument exists
Know when to use single vs. double proportion: single proportion is along one line; double proportion is at the intersection of two lines
Excess and deficiency in sections falls to the north and west boundaries of the township -- this is a classic exam question
An original survey, even if inaccurate, controls over a more accurate resurvey because the original survey created the boundaries
Independent resurveys require Congressional authorization -- if the exam asks about correcting a grossly defective original survey, this is the answer
Closing corners are NOT proportioned -- they are defined by the intersection of survey lines
The 2009 BLM Manual is the current edition and the one tested on the PS exam
When a question describes a corner where "no trace of the original monument remains but local residents remember its location," the corner is obliterated (not lost) because the position can be recovered

PS Exam Preparation

Module 1: Legal Principles

Module 2: Professional Survey Practices

Module 3: Standards & Specifications

Module 4: Business Practices

Module 5: Areas of Practice