---
title: "Intersection method and its advantages"
subject: "Surveying I"
chapter: 6
key: "semester_3/surveying_i:intersection-method-and-advantages"
source: https://www.bctengineer.com/q/semester_3/surveying_i/intersection-method-and-advantages
site: BCT Engineering
---

# Intersection method and its advantages

Surveying I · Chapter 6: Plane Table Survey

- Asked in: 2075 Chaitra, 4 marks; 2072 Chaitra, 2 marks (asked 2 times)
- Video: [Plane Table:  Intersection Method Full](https://www.youtube.com/watch?v=z0wV0VsXdX0) — Dr. Ajay K Gaikwad
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/surveying_i/intersection-method-and-advantages
- Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-6

## Question

What is plane table surveying? Explain the intersection method and its advantages.

## Short answer

Plane table surveying is a graphical method where fieldwork and plotting are done simultaneously on a drawing sheet. In intersection, two stations with a measured base line are used; rays drawn from each station to a point intersect to fix its position, requiring no distance measurement to the point. Advantages: it locates inaccessible points, uses only one linear measurement, allows quick plotting of many points, and provides a check with a third ray.

## Answer

**Plane table surveying** is a graphical method of surveying in which fieldwork and plotting are done at the same time on a drawing sheet fixed on a board (plane table). The plan is drawn to scale directly in the field.

#### Intersection method
Two stations A and B (the ends of a base line) are chosen so that the point P to be located is visible from both.

1. Set the table at A, orient it by compass, and plot **a**. Sight B and draw the ray; measure AB and plot **b** to scale.
2. Sight P from a and draw the ray aP (also rays to the other points).
3. Shift to B, centre **b** over B, and orient the table by back-sighting A along the line ba.
4. Sight P again from b and draw the ray bP. The intersection of the two rays is the plotted point **p**.

```text
                 p
               / |  \
             /   |    \
           /     |      \
         a ------------- b
       (stn A)  base   (stn B)
```

**Advantages:**
- Used for locating inaccessible points (across rivers, hills, buildings, a far-away church spire, etc.) where distance cannot be measured.
- Only one linear measurement (the base line) is needed; many points can be fixed quickly.
- A third ray from another station checks the plotted point.
- Good intersection angle (about 60 to 120 degrees) is needed for accuracy.

## Check yourself

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

1. What is plane table surveying?
   A. A graphical method where fieldwork and plotting are done together on a sheet fixed on a board
   B. An angle measuring method using a vernier circle
   C. A levelling method using a staff
   D. A method using only chain and tape
   Answer: A. Observation and plotting take place at the same time in the field. (Key point: Definition)

2. How is point P fixed by intersection?
   A. By measuring distance AP and BP with a tape
   B. By drawing rays to P from two stations at the ends of a base line; they cut at p
   C. By drawing one ray and scaling a distance
   D. By drawing rays from P to a, b and c
   Answer: B. Two rays from a and b meet at the plotted position p. (Key point: Intersection idea)

3. How is the table oriented at B in intersection?
   A. By eye only
   B. By measuring angle at B
   C. By back-sighting A along the line ba
   D. By trough compass only at B
   Answer: C. At the second station orientation is by back-sighting along the base line. (Key point: Orientation at B)

4. What is the main advantage of intersection?
   A. It needs a measured distance to every point
   B. It cannot be checked
   C. It works only on near points
   D. It locates inaccessible points while only the base line is measured
   Answer: D. Only one linear measurement is needed, and points across rivers etc. can be fixed. (Key point: Advantage)

## Related in Surveying I

- [Intersection versus resection in plane tabling](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aintersection-vs-resection-plane-table) — Surveying I, chapter 6
- [Plane and geodetic surveying; principles](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aplane-geodetic-and-principles) — Surveying I, chapter 1, asked 7×
- [Plane versus geodetic surveying](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aplane-vs-geodetic-surveying) — Surveying I, chapter 1, asked 5×
- [Objectives of surveying; plane vs geodetic](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aobjectives-plane-geodetic) — Surveying I, chapter 1
- [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×
- [Plane table principles; orientation by back sighting](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aorientation-back-sighting) — Surveying I, chapter 6, asked 4×

## Related in other subjects

- [Rankine's method table, 150° intersection, 3°](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Arankine-simple-curve-150-3deg) — Surveying II, chapter 6
- [Coplanar lines, intersection point and plane](https://www.bctengineer.com/question.md?key=semester_2%2Fmathematics%3Acoplanar-lines-intersection-point-plane) — Mathematics, chapter 3, asked 2×
- [Plane through intersection, perpendicular to plane](https://www.bctengineer.com/question.md?key=semester_2%2Fmathematics%3Aplane-through-intersection-perpendicular-plane) — Mathematics, chapter 3
- [Parametric line in 3D: point and plane intersection](https://www.bctengineer.com/question.md?key=semester_4%2Fcomputer_aided_design%3Aparametric-line-segment-plane) — Computer Aided Design, chapter 3