Surveying Notes for SSC JE Civil Engineering
Rahul Kumar
SSC Exam Expert & Content Editor
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Surveying is the science of measuring the relative positions of points on the earth to prepare maps and plans. It is a regular topic in the SSC JE Civil Engineering paper, and most questions are direct from the formulas and the definitions. These surveying notes for SSC JE cover chain surveying, compass surveying, levelling, contours, the theodolite and traversing in simple language with solved examples and practice questions.
Classification of Surveying
| Type | Meaning |
|---|---|
| Plane surveying | The earth's surface is taken as flat; used for small areas (less than about 260 sq km) |
| Geodetic surveying | Curvature of the earth is considered; used for large areas and high accuracy |
| Chain surveying | Only linear measurements are taken, using a chain or tape |
| Compass surveying | Directions are measured with a compass |
| Plane table surveying | Field work and plotting are done together at the site |
| Levelling | Heights (elevations) of points are found |
Chain Surveying
| Item | Detail |
|---|---|
| Metric chain | 20 m chain with 100 links (each link 0.2 m) and 30 m chain with 150 links |
| Gunter's chain | 66 feet long with 100 links |
| Ranging | Fixing intermediate points in a straight line between two end points |
| Offset | The distance of an object from the chain line; perpendicular offsets are the most common |
| Tie line | A line joining two fixed points on the main chain lines to check the accuracy |
| Well-conditioned triangle | Triangle whose angles are between 30 and 120 degrees; the best angle is 60 degrees |
Compass Surveying and Bearings
- Whole Circle Bearing (WCB): measured clockwise from north, from 0 to 360 degrees.
- Quadrantal Bearing (QB): measured from north or south towards east or west, up to 90 degrees.
- Back bearing = fore bearing ± 180 degrees. Add 180 if the fore bearing is below 180, and subtract 180 if it is above 180.
- Magnetic declination: the angle between the true meridian and the magnetic meridian. True bearing = magnetic bearing + declination (east declination is positive).
- Local attraction: the error in the compass because of magnetic materials nearby.
Example 1. The fore bearing of a line is 60 degrees. Find the back bearing.
Back bearing = 60 + 180 = 240 degrees.
Levelling
| Term | Meaning |
|---|---|
| Benchmark (BM) | A fixed point of known elevation |
| Backsight (BS) | First reading taken on a point of known elevation |
| Foresight (FS) | Last reading taken before shifting the instrument |
| Intermediate sight (IS) | Any reading between BS and FS |
| Height of instrument (HI) | Reduced level of the line of sight |
| Reduced level (RL) | Height of a point above the datum |
| Method | Formulas |
|---|---|
| Height of instrument method | HI = RL of BM + BS; RL of a point = HI − FS (or IS) |
| Rise and fall method | Rise or fall = previous reading − present reading; RL = previous RL + rise or − fall |
| Arithmetic check | ΣBS − ΣFS = ΣRise − ΣFall = Last RL − First RL |
Example 2. The RL of a benchmark is 100.000 m and the backsight reading on it is 1.500 m. The foresight on a point is 0.800 m. Find the RL of the point.
HI = 100.000 + 1.500 = 101.500 m, so RL = 101.500 − 0.800 = 100.700 m.
Curvature and refraction correction: combined correction = 0.0673 d² metres, where d is the distance in kilometres (curvature alone is 0.0785 d²).
Contours
- A contour is an imaginary line joining points of equal elevation.
- The vertical distance between two contours is the contour interval, and it is constant for a map.
- Closely spaced contours show a steep slope, and widely spaced contours show a gentle slope.
- Contours never cross each other, except in a overhanging cliff or a cave.
- Contours of a hill are closed with higher values inside, and contours of a depression have lower values inside.
- Contours cross a ridge and a valley line at right angles.
Theodolite and Traversing
- A theodolite measures horizontal and vertical angles; the line of sight is made level by the plate levels.
- A transit theodolite can rotate its telescope fully about the horizontal axis.
- Face left and face right observations are taken to remove instrumental errors.
- A traverse is a series of connected survey lines; it is closed if it ends at the starting point and open if it does not.
- Sum of the interior angles of a closed traverse = (2n − 4) right angles, where n is the number of sides.
- Bowditch rule is used to adjust the closing error of a traverse in proportion to the length of the sides.
Modern Instruments
- Total station: measures angles and distances electronically and stores the data.
- GPS: gives the position of a point using satellites.
- EDM: Electronic Distance Measurement using light or microwaves.
Quick Tips
- Learn the levelling formulas and the arithmetic check, because most numerical questions come from them.
- For bearings, first check if the fore bearing is less than or more than 180 degrees.
- Remember the 20 m chain has 100 links of 0.2 m each.
- Remember that closely spaced contours mean a steep slope.
Quick Revision Points
- Plane surveying treats the earth as flat.
- Back bearing = fore bearing ± 180 degrees.
- HI = RL + BS and RL = HI − FS.
- ΣBS − ΣFS = Last RL − First RL.
- Bowditch rule corrects the closing error of a traverse.
Practice Questions With Answers
- How many links are there in a 20 m metric chain?
Answer: 100 - Find the back bearing of a line with a fore bearing of 120 degrees.
Answer: 300 degrees - What is the formula of the height of instrument?
Answer: HI = RL of BM + BS - What does a contour line join?
Answer: Points of equal elevation - Which rule is used to adjust a closed traverse?
Answer: Bowditch rule - What is the sum of the interior angles of a closed traverse of 6 sides?
Answer: 720 degrees (2 × 6 − 4 = 8 right angles) - What does a close spacing of contours indicate?
Answer: A steep slope - What is the best angle of a well-conditioned triangle?
Answer: 60 degrees - Which instrument is used to measure horizontal and vertical angles?
Answer: Theodolite - A BM has RL 50.000 m and BS 2.000 m. If FS on a point is 1.500 m, find its RL.
Answer: 50.500 m
How to Practise This Chapter
Solve two levelling problems and two bearing problems daily and always check your answer with the arithmetic check. Then solve questions from our practice papers and the previous year papers page. Read the next chapter, Concrete Technology, and see all topics on the SSC JE Civil Engineering notes page. For the other sections of the exam, read the Reasoning notes and General Awareness notes.
Frequently Asked Questions
What is surveying?
Surveying is the science of measuring the relative positions of points on the earth to make maps and plans for construction work.
What is the difference between plane and geodetic surveying?
Plane surveying treats the earth as flat and is used for small areas, while geodetic surveying considers the curvature of the earth for large areas.
What is a benchmark?
A benchmark is a fixed point of known elevation that is used as a reference in levelling.
What is the height of instrument method?
In this method HI is found by adding the backsight to the RL of the point, and the RL of other points is found by subtracting the foresight from HI.
What is the arithmetic check in levelling?
The sum of backsights minus the sum of foresights should be equal to the last RL minus the first RL.
What is a back bearing?
The back bearing of a line is the bearing of the line in the opposite direction. It is the fore bearing plus or minus 180 degrees.
What is magnetic declination?
It is the angle between the true meridian and the magnetic meridian at a place.
What is a contour?
A contour is an imaginary line that joins points of the same elevation above a datum.
What is a traverse?
A traverse is a series of connected survey lines whose lengths and directions are measured.
What is the use of the Bowditch rule?
The Bowditch rule is used to adjust the closing error of a closed traverse in proportion to the lengths of the sides.
Is surveying important in SSC JE Civil?
Yes. Surveying gives a regular set of direct and numerical questions in the Civil Engineering section of Paper I.
How many questions come from surveying in SSC JE?
Usually three to six questions come from surveying, but the number changes from year to year.
Rahul Kumar
SSC Exam Expert & Content Editor
Rahul is a senior SSC exam strategist with 8+ years of experience helping aspirants crack CGL, CHSL and MTS exams. He writes in-depth notification breakdowns, exam pattern guides and preparation strategies.