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Surveying

14 min read

What is surveying?

Surveying is the measurement of distances, angles and heights on the ground to make a plan or map. Surveys are needed for building roads and houses, marking boundaries, and planning farms and cities. Types include chain (tape) surveying, which measures distances only; compass surveying, which measures bearings; levelling, which measures heights; theodolite surveying, which measures angles; and modern GPS and drone surveys.

EquipmentUse
Chain or measuring tapeMeasure distances
Ranging polesMark points and keep a straight line
Arrows (pins)Count the chain lengths
Cross staff / optical squareSet out right angles for offsets
Field bookRecord chainages and offsets
Compass, clinometerMeasure bearings and slopes
PegsMark stations

Chain and tape surveying

A chain line is run between two stations. Features are fixed by measuring the distance along the chain (chainage) and the offset at right angles from the chain. The measurements are recorded in the field book. The survey is plotted at a scale to draw a plan. When measuring on a slope, the horizontal distance must be found: horizontal distance = slope length × cos θ.

Chain survey with offsetsA chain line runs from station A to station B. Features such as a tree, a house corner and a pond are fixed by measuring along the chain to a point, and then measuring a short offset at right angles from the chain to the feature. The chainage and the offset are recorded in the field book.A (0 m)B (120 m)offset 20 m30 m10 m60 mhouse12 mpond95 m

Calculating area

A plot is divided into triangles and trapeziums. The area of a triangle is ½ × base × height. The area of a trapezium is ½ × (sum of the parallel sides) × width.

Worked exampleArea from offsets

A chain line is 100 m long. Offsets taken at intervals of 25 m are 0, 8, 12, 10 and 0 m. Estimate the area between the chain line and the boundary.

  1. Use the trapezoidal rule with width 25 m.

Answer: The area is about 750 m².

The offsets define the boundary of the plot.
Try itSlope correction and area

A tape measures along a slope. Choose the slope length and angle, and the width of a rectangular plot.

Check yourself An offset is measured
Check yourself The equipment that keeps a chain line straight is the
Check yourself For a slope, the horizontal distance is the slope length multiplied by

Key terms

Surveying
Measuring the land to make a map or plan.
Chainage
The distance along the chain line.
Offset
A measurement at right angles from the chain line.
Station
A fixed point in a survey.

Summary

  • Surveying measures distances, angles and heights.
  • A chain survey records chainages and offsets in a field book.
  • The area is found by dividing the plot into triangles and trapeziums.
  • On a slope use the horizontal distance.
Climatic Regions Geography Project