It is necessary that every farmer should have an elementary knowledge of surveying. But in most West African countries, where the majority of farmers are relatively uneducated, it is difficult to explain the importance of simple survey operations. Farm surveying may be defined as the process by which we make measurements on the farm and then represent such measurements by tables, plans or layouts for specific purposes. This definition implies therefore that surveying is, to a large extent, a branch of applied mathematics.

**Units of measurement:**

In surveying, various units of measurement are employed by various people. It is however necessary that there should be some standardisation regarding measurements. Pacing was used traditionally and today it is still in use in some areas. When rough measurements are being undertaken, 1 pace may be assumed to be equal to 1 metre. But, when more accurate measurements are required, the exact relationship between the pace and the metre must be determined. If, for example, 80 metres took 100 paces, then one pace would be equivalent to:

80

------- = 0.8 metres

100

Tapes are also frequently used for measuring short distances. This kind of tape is know as a Surveyor's tape. It is made of either cloth or steel and is usually 20 or 30 metres long. The tape is marked in centimetres. Measurements carried out with this kind of tape are usually accurate. Two people are required to carry out tape measurements. The first man holds the

------- = 0.8 metres

100

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Tapes are also frequently used for measuring short distances. This kind of tape is know as a Surveyor's tape. It is made of either cloth or steel and is usually 20 or 30 metres long. The tape is marked in centimetres. Measurements carried out with this kind of tape are usually accurate. Two people are required to carry out tape measurements. The first man holds the

end of the tape while the second man measures the distances. If the distance to be measured is longer than 30 metres, more than one tape length will be required. At the end of one tape length the man taking the measurement will knock a stick into the ground to indicate that one length has been obtained and the process is repeated until the measurement is completed Some people still use equipment known as the Gunter's Chain to carry out measurements of length.

This chain consists of 100 links and is 22 yards or 20.117 metres long. Each link is therefore 0.20117 metres long. As is the case with tapes, two people are required to carry out chain measurements. The method of measurement is the same as that described for apes. Ranging poles are used to mark the distances measured, each pole being 2.0117 metres long.

**Examples of surveying**

When carrying out surveys, one of the basic operations is to set out a right angle. This technique makes use of the Pythagoras Theorem which states that the square on the hypotenuse is equal to the sum of the squares on the other two sides. Where a tape or a chain is not available, one can make use of a rope of known measurement. It is important to note that the area of an equilateral triangle is obtained by multiplying half the length of the base by the height.

Farm and Example of surveying(Units of measurement)
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March 10, 2022
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