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Lesson Note
Subject: Agricultural science
Topic: Farm Surveying
Learning Objectives: By the end of the lesson, the learners should be able to:
- Define the term farm surveying,
- State the importance of farm surveying,
- Identify some common survey equipment,
- Suggest ways of maintaining common survey equipment.
Lesson Discussions
Farm Surveying can be defined as a process of determining by measurement the positions of features on the farm so that by plotting such measurement to a suitable scale, a map of the farm surveyed may be produced.
Significance/Importance Of Farm Surveying
- Farm surveying enable us produce a map of the area surveyed.
- It helps us determine by measurement the positions of features on the farm and the extent of the agricultural farm land (the hectare of land).
- It helps to determine the nature and type of soils and the land use capability so that the soil is put to the best and maximum use.
- It gives information on the agricultural system to be adopted.
- It makes for appropriate tax assessment and may be required by a bank for loan to be granted.
- It helps to point out limitations on the farm and is required for efficient planning and organizations of the farm stead.
- It help to determine the amount of inputs such as land, seeds, fertilizers, chemicals to be used in the farm.
- Farm surveying also gives the land owner land security.
Common Survey Equipment
- Pegs: Pegs are short wooden poles of about one metre and of square or circular section. They are pointed at one end for easy pushing into the ground. They are used to mark the boundaries of ranged land.
- Matchets: These consist of short wooden or rubber handles with large metal blades and sharpened edges. They are used in cutting down bush or trees during survey.
- Ranging Poles: These are circular poles of about 2.5cm in diameter and 2m long with pointed iron shoes at one end for pushing into the ground. The poles are usually painted red, white or black in bands to make them visible when used in field ranging. The ranging poles are used to define straight lines between two points. This process of using ranging poles to determine a straight line is called ranging.
- Gunter’s Chain: The Gunter’s chain is about 66ft long and is divided into 100 links or units of 0.66ft long each. It is used for direct measurement of a line (lengths) for chaining. Two people are required to carry out ts use.
- Measuring Tapes: These are usually 30m in length and are used in taking direct measurements on a line. That is, measurement of length, breath and height. This process of taking measurement of a line with a measuring tape is called taping. It is marked on one side with metric units and the other side in the imperial units. It is wound in a small case from where it is unwounded for use. Its use requires two people to hold it.
- The Cross Staff: This is an instrument which allows a right angle to be set out with reasonable accuracy. There are two forms. One is a frame with sighting slits at right-angles. The other is in form of a cylinder and is slightly more refined, also has additional slits enabling angles of 45 degrees to be set out as well. Both types are mounted on short ranging rods when in use.
- Offset Staff: This is a graduated rod of 3m to 4m long. A hook may be fitted at the top for the purpose of pulling a chain through a hedge. It is used for taking short offset measurements. Each telescopic link is 0.3m or 30cm in length.
- Chainpins Or Chaining Arrows: These are thin pointed steel wires of about 30cm or 40cm long and about 3mm in diameter with the top bent into a small ring about 40mm in diameter. A red cloth may be attached to the ring so that it can be seen from afar. It is used for making measured length off on the ground. It may also be used for making stations.
- Prismatic Compass: The compass is an instrument designed for the measurement of direction with reference to magnetic meridian. The magnetic meridian is the direction indicated by a freely suspended magnetic needle that is free from local attractions. The compass shows the magnetic north. This magnetic north varies from place to place and differs from the true north. The Prismatic Compass has a magnetic pin pivoted on a non-magnetic object and a metal case with a glass top. The compass needle carries a card that is graduated from 0 degrees to 360 degrees in a clockwise direction. The compass has three poles (tripods) that support it.
- Plain meter: This is an instrument that is used to measures areas mechanically on survey plans.
- Theodolite: It is an instrument designed to measure vertical and horizontal angles. Examples are universal and geodetic theodolites. It consists of the tripod-stand made of wood or light weight metal. The tripod stand forms the base of the instrument. It has a lower plate which contains the graduated horizontal circle made of glass or brass. It has a spirit level which is used to define the horizontal plane against which angles of elevation or depression are measured.
- Levels: The level is an instrument that is used to maintain a horizontal line of sight at a given place. Some classes of levels are dumpy, tilting and automatic levels. One factor that is common to all the levels is the telescope which when properly levelled defines a horizontal line of sight.
Maintenance Of Common Surveying Equipment
Maintenance here refers to the totality of efforts aimed at safeguarding the surveying equipment and prolonging their life. These effort include the following:
- Cleaning the equipment especially after use
- Storing the equipment away from termites. This protects measuring tape, wooden handle of matchets, wooden pegs and tripod stand from destruction by termites.
- Storing them in cool dry places.
- Using the instruments according to the maker’s instruction.
- Sharpening the metal blades of instrument like matchets.
- Oiling the metal parts of instruments where necessary.
- Also, equipment should be used for intended purpose and need not left to lie about.
Done studying? See all previous lessons in Agriculture.
Take a quick test for this lesson
- What do you understand by the term farm surveying?
- State the importance of farm surveying.
- Mention some common survey equipment.
- Suggest ways of maintaining common survey equipment.
Questions answered correctly? Bravo!!
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