Compass Survey or Magnetic Bearing Survey

In land surveying, we use various instruments to map the earth. While Chain Surveying is used for linear measurements, Compass Surveying is employed to measure angular directions.

What is Compass Surveying?

Compass surveying is a branch of surveying in which the directions of survey lines are determined with a magnetic compass, and the lengths of the survey lines are measured with a chain or tape.
The Advantage over Chain Surveying:
In Chain Surveying, the area must be divided into a network of triangles, which can be difficult in areas with obstacles. In Compass Surveying, we measure the angles (bearings) of lines with respect to a known direction. This allows us to plot independent lines, making the process much simpler and more flexible.

Meridian: The reference direction relative to which angles are measured. These are of three types: True, Magnetic, and Arbitrary.
Bearing: The horizontal angle between the meridian and the survey line.

There are two main types of compasses used in surveying:

This is the most convenient type of compass because sighting the object and reading the scale can be done simultaneously.
Graduation: It uses the Whole Circle Bearing (W.C.B.) system, marked from $0^{\circ}$ to $360^{\circ}$ .
Magnetic Needle: Features a broad needle attached to the aluminum graduated ring. The ring does not rotate with the box; the needle stays aligned with the magnetic North.
Reading: The readings are written inverted (upside down) because they are viewed through a prism, which reflects them to appear upright.
Zero Point: The $180^{\circ}$ mark is at the North end, and $0^{\circ}$ (or $360^{\circ}$ ) is at the South end to allow for direct reading through the prism at the observer's end.

In this compass, sighting and reading must be done as two separate steps.
Graduation: It uses the Reduced Bearing (R.B.) or Quadrantal Bearing system, marked from $0^{\circ}$ to $90^{\circ}$ in each quadrant.
Magnetic Needle: Features an "edge-bar" needle that rotates freely over the graduated scale, which is attached to the compass box.
Reading: Readings are taken directly from the top through the glass cover, so the numbers are written upright.
Zero Point: North and South are marked as $0^{\circ}$ , while East and West are marked as $90^{\circ}$ .

Feature Prismatic Compass Surveyor Compass
Reading System Whole Circle Bearing ( $0^{\circ}$ to $360^{\circ}$ ) Reduced Bearing ( $0^{\circ}$ to $90^{\circ}$ )
Graduation Written Inverted Written Upright
Needle Broad needle, attached to the ring Edge-bar needle, rotates freely
Sighting & Reading Simultaneous Separate actions
Tripod Optional (can be used handheld) Mandatory
Prism Present Absent

The primary objective of a compass survey is Traversing (connecting a series of lines).
Selection of Stations: Choose points that are inter-visible (you can see the next and previous stations clearly).
Centering: Set the compass on a tripod exactly over the station peg using a Plumb Bob.
Leveling: Ensure the compass box is perfectly level so the needle can swing freely without touching the glass or the ring.
Sighting and Reading:
Align the Object Vane (horsehair) and Eye Slit with the ranging rod at the next station.
Once the needle settles, take the reading. In a Prismatic compass, look through the prism; in a Surveyor compass, read directly from the top.

As a Civil Engineer, you must be aware of Local Attraction. Since the compass depends on a magnetic needle, its accuracy is disturbed by nearby magnetic objects like:
Power lines or transformers.
Railway tracks.
Iron pipes, steel chains, or keys in your pocket.
How to detect it:
Take both the Fore Bearing (FB) and Back Bearing (BB) for every line.
If $(FB - BB) = 180^{\circ}$, the stations are free from local attraction.
If the difference is not $180^{\circ}$ , a mathematical correction must be applied to the readings.
NTS Study Note: For competitive exams like SSC JE, remember that the Prismatic Compass is favored for quick field work, while the Surveyor Compass is used when Quadrantal Bearings are specifically required for calculations

🏗️ Surveying: Complete Study Guide & Index

Surveying: A Bird's Eye View – Meaning and significance of land surveying.
Fundamental Principles – Classification and types of surveying.
Primary Division – Understanding Plane vs. Geodetic Surveying.
Representative Fraction (RF) – Utilization of scales and reduction factors.

Chain Surveying – Basic procedures and workflow.
Errors & Adjustments in Chaining – Deficiencies in measurement and their remedies.
Distance Measurement Methods – Detailed discussion on linear surveying tools.
Tape Corrections – Adjustments for Sag, Temperature, and Pull.

Compass Surveying – Magnetic bearing survey and its applications.
Plane Table Surveying – Equipment used and graphical methods.
Theodolite Surveying – Horizontal and vertical angle measurement.
Total Station – Components, features, and modern digital use.

Need for Levelling – Why vertical measurement is vital in civil engineering.
Key Concepts: RL & Datum – Definitions of Reduced Level, Datum, and Benchmarks.
Operating Levelling Instruments – Handling Auto Level and Tilting Level.

Remote Sensing – Information on INSAT and IRS Series satellites.
GIS & LIS Systems – Geographic data management and functionality.
Laser Scanning – Advanced application and control.
Geoid & Ellipsoid – Understanding the mathematical shape of the Earth.

Surveying Quiz 1 (01-25) – GPS, Remote Sensing, and Photogrammetry.
Surveying Quiz 2 (26-50) – Ranging, EDM, and Tacheometry.
Surveying Quiz 3 (51-75) – Contouring and HI Method Levelling.
Surveying Quiz 4 (76-100) – Transition Curves and Bowditch Rule.
Surveying Quiz 5 (101-125) – Plane table and Compass
Surveying Quiz 6 (125-150) – Theodolite Surveying and Levelling
Surveying Quiz 7 (151-175) – Tacheometry, Curves, Modern Surveying Instruments (EDM/GPS)
Surveying Quiz 8 (175-200) – Area & Volume Calculation, Minor Instruments

Surveying Top 1-100 One-Liners
Surveying Advanced (101-200) One-Liners
Surveying Master Class (Part 1)
Surveying Master Class (Part 2)
Quick Revision Guide
Quick Surveying Formulas

Surveying IS Codes with Latest Revision Years

Compass Survey or Magnetic Bearing Survey

In land surveying, we use various instruments to map the earth. While Chain Surveying is used for linear measurements, Compass Surveying is employed to measure angular directions.

What is Compass Surveying?

Meridian: The reference direction relative to which angles are measured. These are of three types: True, Magnetic, and Arbitrary.Bearing: The horizontal angle between the meridian and the survey line.

There are two main types of compasses used in surveying:

🏗️ Surveying: Complete Study Guide & Index

Surveying: A Bird's Eye View – Meaning and significance of land surveying.Fundamental Principles – Classification and types of surveying.Primary Division – Understanding Plane vs. Geodetic Surveying.Representative Fraction (RF) – Utilization of scales and reduction factors.

Chain Surveying – Basic procedures and workflow.Errors & Adjustments in Chaining – Deficiencies in measurement and their remedies.Distance Measurement Methods – Detailed discussion on linear surveying tools.Tape Corrections – Adjustments for Sag, Temperature, and Pull.

Compass Surveying – Magnetic bearing survey and its applications.Plane Table Surveying – Equipment used and graphical methods.Theodolite Surveying – Horizontal and vertical angle measurement.Total Station – Components, features, and modern digital use.

Need for Levelling – Why vertical measurement is vital in civil engineering.Key Concepts: RL & Datum – Definitions of Reduced Level, Datum, and Benchmarks.Operating Levelling Instruments – Handling Auto Level and Tilting Level.

Remote Sensing – Information on INSAT and IRS Series satellites.GIS & LIS Systems – Geographic data management and functionality.Laser Scanning – Advanced application and control.Geoid & Ellipsoid – Understanding the mathematical shape of the Earth.

Surveying Top 1-100 One-LinersSurveying Advanced (101-200) One-LinersSurveying Master Class (Part 1)Surveying Master Class (Part 2)Quick Revision GuideQuick Surveying Formulas

Surveying IS Codes with Latest Revision Years

Meridian: The reference direction relative to which angles are measured. These are of three types: True, Magnetic, and Arbitrary.
Bearing: The horizontal angle between the meridian and the survey line.

Surveying: A Bird's Eye View – Meaning and significance of land surveying.
Fundamental Principles – Classification and types of surveying.
Primary Division – Understanding Plane vs. Geodetic Surveying.
Representative Fraction (RF) – Utilization of scales and reduction factors.

Chain Surveying – Basic procedures and workflow.
Errors & Adjustments in Chaining – Deficiencies in measurement and their remedies.
Distance Measurement Methods – Detailed discussion on linear surveying tools.
Tape Corrections – Adjustments for Sag, Temperature, and Pull.

Compass Surveying – Magnetic bearing survey and its applications.
Plane Table Surveying – Equipment used and graphical methods.
Theodolite Surveying – Horizontal and vertical angle measurement.
Total Station – Components, features, and modern digital use.

Need for Levelling – Why vertical measurement is vital in civil engineering.
Key Concepts: RL & Datum – Definitions of Reduced Level, Datum, and Benchmarks.
Operating Levelling Instruments – Handling Auto Level and Tilting Level.

Remote Sensing – Information on INSAT and IRS Series satellites.
GIS & LIS Systems – Geographic data management and functionality.
Laser Scanning – Advanced application and control.
Geoid & Ellipsoid – Understanding the mathematical shape of the Earth.

Surveying Top 1-100 One-Liners
Surveying Advanced (101-200) One-Liners
Surveying Master Class (Part 1)
Surveying Master Class (Part 2)
Quick Revision Guide
Quick Surveying Formulas