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Types of errors in surveying
Short answer
Mistakes are large, avoidable blunders. Errors are systematic (cumulative, same sign, correctable, e.g., tape too long) or accidental (random, compensating, reduced by averaging, e.g., reading fractions). They arise from personal, instrumental or natural sources.
Describe the various types of errors in surveying (differentiate errors and mistakes; cumulative and random/accidental errors) with examples.
An error is the difference between a measured value and its true value. No measurement is free from error.
Mistakes (blunders) and errors
| Mistake (blunder) | Error |
|---|---|
| Caused by carelessness or lack of knowledge | Caused by imperfect instruments, methods and nature |
| Large in size, can be avoided | Small and unavoidable, but can be reduced |
| Examples: wrong booking, miscounting tape lengths, reading 5.4 as 4.5 | Examples: tape expansion, reading estimate |
| Found by checks and repeating | Corrected by calculation or adjusted |
Types of errors
1. Cumulative (systematic) errors. These have the same sign in all measurements and increase with the amount of work. Their size and sign can be found and a correction applied.
- Examples: tape too long or short, a wrong zero in a levelling staff, sag, temperature change, collimation error in a theodolite.
2. Accidental (random or compensating) errors. These occur due to causes beyond the surveyor's control and are equally likely to be positive or negative. They follow the laws of probability and are reduced by repeating the measurements and taking the mean.
- Examples: estimating the last fraction of a reading, slight movement of the plumb bob, personal limitations of eyesight.
By source
- Personal errors: due to the observer (limited sight, bias, careless reading).
- Instrumental errors: due to imperfect adjustment or construction of the instrument.
- Natural errors: due to wind, temperature, refraction, curvature of the earth.
Systematic errors are removed by calibration and corrections, and accidental errors are minimised by taking many observations.
✓ Answer checked by Claude Opus 5.5 (high effort)
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