Types of Chain Surveying
🔍 Definition: What is Chain Surveying?
Chain surveying is the branch of surveying in which only linear measurements are made in the field, using a chain, tape, or steel band. The area is divided into a network of triangles based on the principle of triangulation. All sides of the triangles are measured directly, and angles are either calculated or plotted graphically. This method is simple, economical, and suitable for small, open, and fairly level areas.
❓ Why use Chain Surveying?
Chain surveying is used because it requires no expensive instruments, delivers quick results, and is ideal for small projects such as building sites, gardens, and preliminary road surveys. Its fundamental principle is to work from whole to part — first establish a large triangular framework, then fill in interior details using offsets.
🛠️ Instruments Used in Chain Surveying
Besides the chain itself, several accessories are essential:
- Chain (various types – detailed below).
- Tapes (linen, steel) – for measuring short distances or offsets.
- Arrows – 10 steel arrows, used to mark the end of each chain length.
- Ranging rods – 2-3 m long, coloured bands, used to establish straight lines.
- Offset rod – similar to ranging rod but with a hook for pulling chain/tape.
- Pegs – to permanently mark stations.
- Plumb bob – for transferring points on sloping ground.
- Field book – for recording measurements and sketches.
🔗 Types of Chains used in Chain Surveying (Classification)
The chain is the backbone of chain surveying. Below are the five main types:
| Chain Type | Length | Links & Link Size | Material & Handles | Primary Use / Region |
|---|---|---|---|---|
| Metric Chain | 5, 10, 20, 30 metres | 100 links; each 0.2 m (20 cm) for 20 m chain | Galvanized steel, brass handles, tallies every metre | Metric system countries; most common |
| Gunter’s Chain | 66 feet (20.1168 m) | 100 links; 1 link = 0.66 ft (7.92 inches) | Steel links, brass handles, tallies every 10 links | British imperial; area in acres (10 sq. chains = 1 acre) |
| Engineer’s Chain | 100 feet (30.48 m) | 100 links of 1 ft, or 50 links of 2 ft | Heavy steel, swivel handles | Roads, railways in US/UK; decimal feet |
| Revenue Chain | 33 feet (10.0584 m) | 16 links; each 2.0625 ft | Similar to Gunter’s but shorter | Land revenue surveys in India; small fields |
| Steel Band / Band Chain | 20, 30, 50 metres | Continuous ribbon, graduated every 20 cm or 0.5 ft | Tempered steel, wound on a handle | High precision, baseline measurement |
🔺 Types Based on Triangulation Configuration
Triangles with all angles between 30° and 120°. These are ideal because small errors in side measurement have minimal impact on plotting. Equilateral triangles are considered the best.
Triangles having any angle less than 30° or greater than 120°. These are avoided because even a small measurement error can cause large plotting distortions.
🧭 How to conduct Chain Surveying? (Step-by-Step)
Step 1 – Reconnaissance: Walk the area, select stations ensuring well‑conditioned triangles.
Step 2 – Marking Stations: Drive pegs or place ranging rods. Name stations (A, B, C,…).
Step 3 – Ranging: Establish intermediate points on a straight line between two stations.
Step 4 – Chaining on Level Ground: Leader and follower stretch the chain, insert arrows at each chain length. Count arrows to find total distance.
Step 5 – Chaining on Slopes: Use the stepping method (breaking into horizontal segments) or measure slope angle and apply correction H = L cosθ.
Step 6 – Offsets: Measure perpendicular or oblique distances from the chain line to detail points (building corners, fences).
Step 7 – Booking: Record measurements and sketches in a field book.
Step 8 – Plotting: Draw triangles to scale, then plot offsets to create a detailed map.
🚧 Obstacles in Chain Surveying and Solutions
- Obstacle to ranging (only visibility blocked): Hill or mound – use reciprocal ranging.
- Obstacle to chaining (pond, river): Use geometric constructions (similar triangles) to find distance.
- Obstacle to both (building): Create parallel offset lines to go around it.
📉 Errors in Chain Surveying and Minimization
Instrumental Errors: Chain too long or short. Correction = (measured length) × (error per chain).
Personal Errors: Miscounting arrows, poor ranging – reduce by careful work and re-measurement.
Natural Errors: Temperature expansion, wind – control tension, apply temperature correction if needed.
Slope Correction: If slope angle θ, horizontal distance = measured length × cosθ.
✅ Advantages of Chain Surveying
- Simplicity: No angle measurement needed.
- Economical: Only chain, tape, and few accessories required.
- Fast: Quick results for small, open areas.
- Self-checking: Triangles provide inherent accuracy checks.
❌ Disadvantages of Chain Surveying
- Unsuitable for large, undulating, or wooded areas.
- Errors accumulate if chain is not standardized.
- Requires well‑conditioned triangles – may need many stations.
- No angular control – small errors may go undetected.
📍 Uses / Applications of Chain Surveying
This method is still used for small building sites, gardens, preliminary surveys for roads in flat areas, revenue records (using revenue chain), archaeological sites, military training, and practical classes in engineering colleges.
🛡️ Is Chain Surveying Safe?
Yes, it is one of the safest surveying methods. It involves no electricity, lasers, or heavy machinery. However, precautions are advisable: wear gloves to avoid cuts from old chains; wear bright clothing when working near roads; be careful on slopes. With common sense, it is completely safe.
Frequently Asked Questions (FAQ)
📘 Additional Important Facts
Chain Surveying vs. Compass Surveying: Chain surveying measures only linear distances, while compass surveying measures bearings (angles). Chain surveying is more accurate in flat, open areas.
This article is fully detailed and optimized for PDF/print. No header/footer/menu included.