Compass Surveying (in Civil Engineering)

1. Definition

Compass surveying is a method of surveying in which the directions (bearings) of survey lines are measured using a magnetic compass, and the lengths of lines are measured using a chain or tape.
It is mainly used to prepare plans of small areas where very high accuracy is not required.

2. Instruments Used

Prismatic Compass or Surveyor’s Compass – to measure bearings
Chain or Tape – to measure distances
Ranging rods – to mark stations
Arrows / pegs – to mark chain lengths
Field book – to record observations

3. Principle

Compass surveying works on the principle of:

Traversing, where a series of connected lines form a traverse.
Each line has:
- A length
- A bearing (angle with respect to North)

Using these two values, the position of each point is plotted on a map.

4. Types of Bearings

Whole Circle Bearing (WCB)
- Measured clockwise from North
- Ranges from 0° to 360°
- Used in prismatic compass
Quadrantal Bearing (QB)
- Measured from North or South toward East or West
- Ranges from 0° to 90°
- Example: N 30° E, S 45° W

5. Steps in Compass Surveying

Reconnaissance
- Study the area and select suitable stations.
Marking Stations
- Fix stations using pegs or rods.
Measuring Bearings
- At each station, measure the bearing of the next line using a compass.
Measuring Distances
- Measure the length of each line using a chain/tape.
Recording in Field Book
- Enter bearings and distances clearly.
Plotting
- Draw the traverse on paper using scale and bearings.

6. Errors in Compass Surveying

(a) Instrumental Errors

Blunt pivot
Bent sight vane
Weak magnetic needle

(b) Natural Errors

Local attraction (nearby steel, electric lines, vehicles, etc.)
Changes in Earth’s magnetic field

(c) Personal Errors

Incorrect reading
Carelessness in booking data

7. Advantages

Simple and quick method
Cheap equipment
Suitable for rough surveys
Useful in hilly and forest areas
Does not require line-of-sight between distant points

8. Disadvantages

Less accurate than theodolite survey
Affected by magnetic disturbances
Not suitable for large projects
Errors increase in industrial areas

9. Applications

Surveying small plots of land
Preliminary surveys for roads and canals
Forest and hilly area surveys
Boundary surveys in villages

10. Examples

Example 1: Simple Traverse Survey

A surveyor measures a small playground using compass surveying.

Line	Distance (m)	Bearing (WCB)
AB	40	45°
BC	30	135°
CD	40	225°
DA	30	315°

Using these values, the surveyor plots a closed traverse and prepares the layout of the playground.

Example 2: Road Alignment

Before constructing a village road, engineers conduct a compass survey to:

Fix direction of the road
Measure approximate distances
Prepare a rough alignment plan

This helps in deciding the best route before detailed surveying is done.

Example 3: Boundary Survey of a Field

A farmer wants to mark boundaries of his land:

Surveyor uses compass to find bearings of boundary lines
Measures each side using chain
Prepares a sketch showing exact directions and lengths

This plan is used for land records and dispute resolution.

11. Difference Between Compass Survey and Theodolite Survey

Feature	Compass Survey	Theodolite Survey
Accuracy	Low	High
Instrument	Compass	Theodolite
Cost	Cheap	Expensive
Magnetic effect	Affected	Not affected
Use	Small surveys	Large engineering works

3.Comass Surveying