Part III — Surveying

Chapter 3: Surveying Fundamentals

3.1 Chain Surveying

Chain surveying is the simplest method of surveying, suitable for small, fairly flat areas with few details, using only linear measurements (no angular measurements). A standard Gunter's chain is 66 feet (20.12 m) long with 100 links; a metric chain is commonly available in 20 m or 30 m lengths with 100 or 150 links respectively. Offsets are measurements taken perpendicular (or at a known angle) from the chain line to locate nearby features; offsets should generally be kept short to minimise error, with a maximum recommended length that depends on the required accuracy.

3.2 Compass Surveying

A prismatic compass is used to measure the bearing of survey lines directly, using the earth's magnetic field. True bearing is measured from the true (geographic) north, while magnetic bearing is measured from magnetic north; the angle between them, called magnetic declination, varies by location and changes slowly over time. Whole Circle Bearing (WCB) system measures bearings from 0° to 360° clockwise from north, while the Quadrantal Bearing (QB) system measures bearings within each 90° quadrant (NE, SE, SW, NW) from either north or south.

3.3 Levelling

Levelling determines the relative heights (elevations) of points on the earth's surface, typically using a dumpy level (or modern auto/digital levels) and a levelling staff. Key terms: Bench Mark (BM) — a point of known/assumed elevation used as reference; Reduced Level (RL) — the elevation of a point relative to a datum; Backsight (BS) — the first staff reading taken from an instrument station, typically on a point of known elevation; Foresight (FS) — the last staff reading taken from an instrument station, typically on a point whose elevation is to be determined; Intermediate Sight (IS) — any staff reading taken between the backsight and foresight from the same instrument station. The Height of Instrument (HI) method and Rise and Fall method are the two standard methods of reducing levels from field readings.

3.4 Theodolite Surveying and Modern Methods

A theodolite measures both horizontal and vertical angles with high precision, used for triangulation, setting out curves, and precise angular control. Modern surveying increasingly uses the Total Station (an electronic instrument combining electronic theodolite and Electronic Distance Measurement, EDM, capable of directly computing coordinates) and GPS/GNSS-based surveying for large-scale and high-precision work, alongside traditional methods still tested in exams for conceptual understanding.

3.5 Practice Set — Surveying (16 MCQs)

1. Chain surveying is most suitable for:
   (a) Large, hilly, and heavily detailed areas (b) Small, fairly flat areas with few details (c) Only underwater surveying (d) Only aerial surveying
2. A Gunter's chain has a standard length of:
   (a) 20 m (b) 30 m (c) 66 feet (20.12 m) (d) 100 feet
3. Offsets in chain surveying are measurements taken:
   (a) Along the chain line only (b) Perpendicular (or at a known angle) from the chain line to locate features (c) Only using a compass (d) Only using a theodolite
4. A prismatic compass is primarily used to measure:
   (a) Vertical angles (b) Bearings of survey lines (c) Elevations (d) Distances directly
5. The angle between true north and magnetic north is called:
   (a) Magnetic declination (b) Bearing angle (c) Azimuth (d) Whole circle bearing
6. In the Whole Circle Bearing (WCB) system, bearings are measured:
   (a) From 0° to 90° only (b) From 0° to 360° clockwise from north (c) From 0° to 180° only (d) Counter-clockwise from south
7. A Bench Mark (BM) in levelling refers to:
   (a) A point of known/assumed elevation used as reference (b) The highest point in a survey area (c) An instrument station only (d) A type of theodolite
8. Reduced Level (RL) refers to:
   (a) The horizontal distance between two points (b) The elevation of a point relative to a datum (c) The angle of a survey line (d) The length of an offset
9. Backsight (BS) in levelling refers to:
   (a) The last staff reading taken from an instrument station (b) The first staff reading taken from an instrument station, typically on a point of known elevation (c) A reading taken only at the end of the survey (d) A horizontal angle measurement
10. Foresight (FS) in levelling refers to:
    (a) The first staff reading from an instrument station (b) The last staff reading from an instrument station, typically on a point to be determined (c) A backward-facing angle (d) A type of bench mark
11. Which of the following is a standard method of reducing levels from field readings?
    (a) Height of Instrument (HI) method (b) Whole Circle Bearing method (c) Fineness Modulus method (d) Bulking method
12. A theodolite is primarily used to measure:
    (a) Only linear distances (b) Both horizontal and vertical angles with high precision (c) Only elevation differences (d) Only magnetic bearings
13. A Total Station combines an electronic theodolite with:
    (a) A magnetic compass (b) Electronic Distance Measurement (EDM) (c) A dumpy level only (d) A chain and tape
14. Intermediate Sight (IS) in levelling refers to:
    (a) A staff reading taken between the backsight and foresight from the same instrument station (b) The very first reading of the entire survey (c) A reading taken only with a theodolite (d) The final reading of the survey
15. The Quadrantal Bearing system measures bearings within each quadrant relative to:
    (a) East and west only (b) North or south, up to 90° (c) A fixed 360° clockwise reference only (d) The zenith
16. GPS/GNSS-based surveying is primarily valued for:
    (a) Being usable only indoors (b) Large-scale and high-precision positioning work (c) Replacing the need for any ground control points ever (d) Measuring only vertical angles

Answer Key

1.(b)

2.(c)

3.(b)

4.(b)

5.(a)

6.(b)

7.(a)

8.(b)

9.(b)

10.(b)

11.(a)

12.(b)

13.(b)

14.(a)

15.(b) 16.(b)