2. Chain Survey

1. What is Chain Survey?

Chain surveying is a method in which only linear measurements are taken in the field using a chain or tape, and the details are plotted later on paper using geometrical constructions.

No angular measurements are taken—only distances.

2. Principle of Chain Survey

It works on the principle of triangulation:

The area is divided into a network of well-conditioned triangles.
A triangle is well-conditioned if no angle is less than 30° and none is more than 120°.
This ensures accuracy and easy checking of measurements.

3. Instruments Used

Chain / Tape – for measuring distances
Ranging rods – to align straight lines
Arrows (pins) – to mark chain lengths
Pegs – to mark survey stations
Cross-staff / Optical square – for setting right angles
Field book – for recording measurements

4. Main Terms in Chain Survey

Survey stations – Fixed points that define the framework
Main stations – Important stations forming the main triangles
Tie stations – Points used to locate interior details
Check lines – Lines used to check accuracy
Base line – The longest main line, measured very carefully
Offsets – Short measurements taken from the chain line to locate details

5. Procedure of Chain Survey

Step 1: Reconnaissance

Walk over the area.
Select suitable main stations.
Plan the layout of triangles.

Step 2: Marking Stations

Fix stations with pegs.
Ensure good intervisibility.

Step 3: Ranging

Align stations using ranging rods.

Step 4: Chaining

Measure distances between stations using chain/tape.
Record in field book.

Step 5: Taking Offsets

Measure offsets to locate features like buildings, roads, trees, etc.

Step 6: Plotting

Draw the survey on paper using recorded measurements.

6. Types of Offsets

Perpendicular offsets – Taken at 90° to the chain line
Oblique offsets – Taken at an angle other than 90°

7. Advantages of Chain Survey

Simple and easy to understand
Cheap and economical
Requires less skill
Suitable for small projects
Good for teaching basic surveying principles

8. Disadvantages of Chain Survey

Not suitable for large areas
Not accurate on uneven or hilly ground
Difficult in crowded areas
Errors accumulate easily
No angular measurements, so precision is limited

9. Applications of Chain Survey

Small plots and fields
Building sites
Roads and canals (small stretches)
Preliminary surveys
Farm land measurement

10. Example in Civil Engineering

If a civil engineer wants to survey a small residential plot for construction:

They use chain survey to measure boundaries.
Take offsets for existing structures.
Prepare a simple site plan for layout and estimation.