Survey Plan and Area Calculation: A Cursory Look

Saji Koduvath, Advocate, Kottayam.

Introduction

A survey plan shows the shape and size of a property. It also helps to calculate the area of the land. Section 82 of the Bharatiya Sakshya Adhiniyam, 2023, provides as under:

  • “82. Presumption as to maps or plans made by authority of Government: The Court shall presume that maps or plans purporting to be made by the authority of the Central Government or any State Government were so made, and are accurate; but maps or plans made for the purposes of any cause must be proved to be accurate.”

A proper survey commission report, supported by a correct and reliable survey plan, is indispensable for the effective adjudication of a large number of civil disputes. Courts and advocates should have a general idea and understanding of surveys and survey plans.

F-lines and G-lines

In survey plans, two types of lines are commonly seen—continuous lines and broken (or dashed) lines. Alongside the survey plan, we also see the field book (or ladder).

Continuous lines show the outer Field-lines (F-lines) of the plot.

Broken lines in a survey plan represent the Guidelines (or Baselines) called G-lines drawn from one bend or a corner of the plot to an opposite bend or corner.

  • The purpose of a G-line is to measure the perpendicular distances (offsets) from the G-line to the boundary bends on either side of the G-line. It is for dividing the land into imaginary right-angle triangles (triangles with one angle of 90 degrees) or trapeziums (four-sided quadrilaterals, two sides of which lie parallel), enabling the area to be calculated in a simple and systematic manner.
  • In surveying practice, these internal G-lines are fixed first, as an axis, and the measurement begins from the starting point of a G-line.

In the case of a large plot, there may be more than one G-line with a view to making the entire plot into triangles or trapeziums.

Offsets Fixed with the Cross-Staff

In surveying, the cross-staff is used to measure the offsets (perpendicular distances from the G-lines to the boundary bends). The cross staff is used to ensure a 90-degree angle for every offset.

Calculation of Area

Each triangle and trapezium, stated above, is shaped in the following manner:

  • Triangle: The required portion of the G-line will be its one side; the offset measurement will be the second side; and the outer field boundary (F-line) will be the third side.
  • Trapezium: Apart from the G-line portion and the outer boundary, two (parallel) offsets are taken into consideration for forming the four sides.

The area of a right-angle triangle is calculated using Heron’s formula. It is:

  • Area = ½ base × altitude.

The area of certain parts (triangles that are not right-angle triangles) may have to be calculated with the side measurements of the triangles. The formula applied in such a case, with side measurements a, b and c, is the following:

  • A = √[s(s-a)(s-b)(s-c)]
  • ‘s’ is the semi-perimeter of the triangle given by s = ½ of (a + b + c).

In certain cases, a portion of the area between two G-lines may need to be calculated by drawing (and measuring) a diagonal (check line) to form two triangles.

Trapeziums are formed between two G-lines or between two offsets. The area of a trapezium is calculated using the following formula:

  • A = ½ of (a + b) × h, where a and b are the lengths of the parallel sides and h is the perpendicular distance between them (required length of the G-line).

Surveying Steps Taken by the Surveyor

The surveyor follows these steps:

  • A rough sketch (draft) of the plot is prepared.
  • One or more G-lines are fixed and drawn in the sketch. The beginning and end points of each G-line are shown with letters (A–B; if there are multiple G-lines, they are placed as C–D, E–F, and so on).
  • To fix and measure the offset length — from the G-line to the boundary-bend (which are marked L, M, N, O, P, etc.) — the cross-staff is used. Flags will be placed at the starting and end points of the G-line, and also at the bend. The surveyor aligns the cross-staff along the G-line by sighting (i) the beginning and end points of the G-line through the slit of the cross-staff and (ii) the required outer bend through the opposite cross-slit.
  • After fixing the cross staff as stated above, the distance (i) from the beginning point of the G-line to the position of the cross staff, (ii) the distance from the outer bend to the G-line (position of the cross staff), and (iii) the outer boundary forming the third side of the triangle, or the fourth side of the trapezium are measured, and the measurements are duly entered in the diagram.
  • In this manner, all offsets—namely, the distances measured from the bends to the G-lines —and the lengths of the outer field boundaries, are taken and recorded in the sketch.

Field Book or Ladder

The field book is usually recorded in the following pattern:

D (75.0)
69.02.0T
68.027.0S
43.07.0R
38.015.0Q
23.02.0P
16.07.0O
10.05.0N
5.05.0M
C
B
(192.0)
L11.0190.0
M14.0188.0
N15.0157.08.0Z
O13.0132.028.0Y
P13.0124.020.0X
Q10.0115.028.0W
R12.0100.0 26.0 V
 S1 3.088.032.0U
 T1 3.076.024.0D
U110.049.0 
V110.027.0  
  4.06.0C
2.03.0L
  A  

It is prepared in the following manner:

  • AB and CD are G-lines.
  • At the bottom, the starting point (alphabet A) of the G-line (AD) is entered.
  • Above it, the distance from the point A to the first offset point on the G-line (2.0 metres) is written.
  • Since the first offset (first bend) is towards the right, the offset distance (3.0 metres) is entered in the right-hand column, and the corresponding boundary bend (L) is stated in the further right column.
  • The second offset (second bend) is also towards the right, the offset distance (6.0 metres) is entered in the right-hand column, and the corresponding boundary bend (C) is stated in the further right column.
  • The third offset being 27 meters away from the point A, and the length of the offset is 10 meters, these matters are also entered.
  • In this manner, entire boundary points (letters L to Z1) and the offset points and measurements are entered.
    • Note: If a and b are the sides of the 90-degree angle of a rectangle triangle, the length of the opposite side (hypotenuse) will be √[a2 + b2]. It is represented by: c2 = a2 + b2.
    • The measurements of all the trapeziums can be checked, applying the formula: c2 = a2 + b2 (after measuring/ drawing the diagonals, or check-lines, in these trapeziums).

Area Calculation

  • Areas of all the triangles and trapeziums are calculated using the required formula.
  • Finally, the areas (all triangles and trapeziums) are added together to get the total extent of the property.

Read also:

End Notes:

Accuracy Presumed on Govt. Maps and Plans u/s 82 BSA (83, IEA)

In Dnyaneshwar Balu Patole v State of Maharashtra, 2011 AllMR(Cri) 1889; 2011-4 MhLJ(Cri) 208, it is held as under:

  • “From the language of section 83 (IEA), it is clear that Court shall presume that the maps or plans purporting to be made by the authority of the Central Government or any State Government were so made and are accurate but maps or plans made for the purposes of any cause must be proved to be accurate. It shows that when plans of town or area or certain roads, forests, rivers, nalas, etc. are prepared for public record and general information there is presumption of its accuracy. However, when a map is prepared for particular cause or purpose, there is no presumption of accuracy and that map has to be proved by leading necessary evidence. If a map is prepared by the investigating agency to prove scene of offence ,that map is prepared for the particular purpose, i.e., to establish scene of offence and certain facts, which the prosecution wants to establish, there can not be any presumption of accuracy to such map. Such map will have to be proved like any other fact by leading necessary evidence.”

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1 Comment

  1. sensationallyllamaa53656cf3d's avatar sensationallyllamaa53656cf3d says:

    Such a useful information Mr. Saji. Great thank you.

    Like

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