---
title: "Ranging across high ground"
subject: "Surveying I"
chapter: 3
key: "semester_3/surveying_i:ranging-intervisible-points"
source: https://www.bctengineer.com/q/semester_3/surveying_i/ranging-intervisible-points
site: BCT Engineering
---

# Ranging across high ground

Surveying I · Chapter 3: Chain Survey

- Asked in: 2062 Poush, 4 marks; 2058 Chaitra, 6 marks; 2079 Bhadra, 3 marks (asked 3 times)
- Video: [Indirect Ranging || 3 D Animated Video || Surveying](https://www.youtube.com/watch?v=0aXX4jNg2EQ) — Civil Samajh
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/surveying_i/ranging-intervisible-points
- Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-3

## Question

Define ranging. Explain how a survey line is ranged between two points that are not intervisible due to intervening high (raised) ground; explain the procedure with a neat sketch.

## Short answer

Ranging is establishing intermediate points on a straight line between two end stations. When ends are non-intervisible due to high ground, reciprocal ranging is used: two assistants on the high ground alternately align each other onto the line between A and B, then intermediate points are set by direct ranging.

## Answer

**Ranging** is the process of establishing intermediate points on a straight line between two end stations so that the chain or tape can be laid in a straight line along them. It is done with ranging rods (direct ranging) when the ends are intervisible, and by **reciprocal ranging** when they are not.

#### Ranging when the ends are not intervisible
When the points A and B are on opposite sides of a hill (high ground), a person at A cannot see B. In this case **reciprocal ranging** is used.

#### Procedure
1. Fix ranging rods at A and B.
2. Choose two points M1 and N1 on the high ground, close to the line AB, such that from M1 both N1 and B can be seen, and from N1 both M1 and A can be seen.
3. Two assistants stand at M1 and N1. The assistant at M1 directs the one at N1 to move to N2 on the line M1B.
4. Then the assistant at N2 directs M1 to move to M2 on the line N2A.
5. The process is repeated (M2 directs N2 to N3 on the line M2B, and so on) until M, N, A and B all lie on one straight line.
6. Once M and N are fixed, intermediate points between A and M, M and N, and N and B are fixed by direct ranging.

```text
          M1 ........ N1
        /     hill     \ 
   A  /                  \  B
   (A, M, N, B finally in one line)
```

The line is then chained over the high ground in the usual way.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is ranging?
   A. Measuring the length between two stations
   B. Establishing intermediate points on a straight line between two end stations
   C. Finding the height of one station above another
   D. Measuring the offset of an object
   Answer: B. Ranging aligns intermediate points so the chain lies in a straight line. (Key point: Definition of ranging)

2. Why is reciprocal ranging used for ends A and B on opposite sides of a hill?
   A. The line is too long for a chain
   B. The ground is too soft for pegs
   C. A and B are not intervisible, so direct ranging cannot be done
   D. Ranging rods are not tall enough
   Answer: C. Direct ranging needs the ends to be visible; reciprocal ranging uses two helpers who direct each other. (Key point: Method used)

3. Which condition must hold for the points M1 and N1?
   A. Both are exactly on the line AB at the start
   B. Both are at the hill's summit and see A and B
   C. Both are at A and B
   D. From M1 both N1 and B are visible, and from N1 both M1 and A are visible
   Answer: D. They are placed close to the line so each can see the other and one end station. (Key point: Positions of helpers)

4. When is the repeated alternate directing stopped?
   A. When M, N, A and B lie in one straight line
   B. After exactly three trials
   C. When M1 and N1 are 30 m apart
   D. When the hill is levelled
   Answer: A. Each cycle improves alignment until the two helper points are on line AB. (Key point: When the process stops)

## Related in Surveying I

- [Prolonging line past a high building](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aobstacle-high-building-prolong-line) — Surveying I, chapter 3
- [Length of PQ across a pond](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aobstacle-pond-chain-line) — Surveying I, chapter 3
- [Methods of plane table survey](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Amethods-of-plane-table-survey) — Surveying I, chapter 6, asked 6×
- [Reciprocal levelling across river, 250 m](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Areciprocal-leveling-river-250m-eyepiece-height) — Surveying I, chapter 5
- [Chain survey principle and operations](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Achain-principle-and-field-procedure) — Surveying I, chapter 3, asked 2×
- [Chainage of R across a river](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aobstacle-river-chainage-of-r) — Surveying I, chapter 3

## Related in other subjects

- [Updating information across survey stages](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Ainfo-updated-stages) — Transportation Engineering I, chapter 2, asked 3×
- [Voltage across string discs is not uniform](https://www.bctengineer.com/question.md?key=semester_4%2Fpower_system_analysis_i%3Astring-voltage-not-uniform) — Power System Analysis I, chapter 2, asked 3×
- [Traverse field procedure between two known stations](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Atraverse-field-procedure-between-known-stations) — Surveying II, chapter 1
- [E due to line charge using Gauss's law](https://www.bctengineer.com/question.md?key=semester_3%2Felectromagnetism%3Aline-charge-field-gauss-law) — Electromagnetism, chapter 2, asked 3×