TOPIC 4: ELEMENTARY SURVEY AND MAP – GEOGRAPHY FORM THREE
Meaning and Types of Survey
Simple Land Survey
Explain the meaning of simple land survey
Surveying is the science of measuring and record distances, angles and heights on the Earth‘s surface to obtain data from which accurate plans and maps are made.
Surveying is also the art and science of making or taking measurements both linear and angular on the Earth‘s surface at different positions for the purpose of producing a plan or map.
Angular measurement means measuring the distance from a given reference point to an observed object. The distance is measured in a clockwise direction from North.
Linear measurement is the distance measured along the surface of the ground such as a horizontal distance.
Purpose of surveying
- To prepare maps and plans
- To calculate areas and distance
Types of Simple Land Survey
Explain the types of simple land survey
Surveying can becategorisedinto various types or branches depending on its purpose, function and nature.
Thetypes or branches include:
i. Topographical survey
This kind of survey is carried out for the purpose of preparing topographical maps.
ii. Geodetic survey
This kind of survey is carried out with the aim of knowing the Earth‘s shape and size (the Earth’s configuration)
iii. Cadastral survey
This kind of survey is conducted with the aim of preparing a legal document such as house plans, town or city boundaries, etc. It is mainly used for ownership purposes.
iv. Engineering surveys
This kind of survey is conducted for the building and construction layout of railways, bridges and roads.
v. Geological survey
This kind of survey is conducted with the aim of knowing the distribution of rocks and minerals under the Earth‘s surface.
TOPOGRAPHICAL SURVEYING
This kind of survey is carried out for the purpose of preparing topographical maps.Topographical maps are those maps whose contents include both man-made features such as linear features (roads, railways, telephone lines, water systems, and electricity poles) and natural features such as rivers, oceans, mountains, etc.
The topographical survey has the following ways or methods of conducting the survey:
- Chain or tape survey;
- The prismatic compass survey;
- The plane table survey;
- The technique of levelling.
Chain/Tape Survey
Describe chain/tape survey
It is a method of Surveying in which no angles are measured but only linear measurement is taken in the field by using a chain or tape measure.It measures a series of straight lines on the ground with a chain or tape measure and all fixed points relative to theline of traverseeither by right angles (offsets) ortie lines.
Types of Equipment used in Chain/Tape Surveying
Explain different types of equipment used in chain/tape surveying
Chain
- Thechainis made up of steel wire which is divided intolinksandtogs(rings) to facilitate folding.
- It is sometimes used as a unit of measurement
- It has brass handles at both ends for easy handling. The link is 0.2m or 200mm in diameter.
- The length is 20m or 30m.
Tape
- Steel tape
- Linear tape
Atapeis made from fiberglass or a steel strip and is 10m, 20m or 30m in length graduated in 10mm divisions and numbered at each 100mm (10) divisions.It is used for measuring short distances
Ranging poles
Ranging polesare made up of wood or light metal and measure about 2m long at the top. The equipment has steel shades on its legs so it can be stuck into the ground. Ranging poles are painted red and white so that they can be easily seen even from a distance. They are used for making stations.
Arrows
Arrowsare made of steel wire of diameter 4mm and their ends are bent into a circle where red cloth is tied to facilitate visibility. They are used for showing points on the ground.They are also used for counting the number of chains while measuring a chain line.
Pegs
Pegsare made of wood 40mm square by 50cm long and are used for permanently marking positions during survey
Surveyors’ band
Thesurveyor’s bandis made of a steel strip which is rolled into a metal frame with a winding handle. It is 30m, 50m or 100m long. Is used in projects where more accuracy measurement is required.
Cross staff
Thecross staffis made of metal or wood witheye slipsat right angles and is used to measure right angles from the line of traverse
Notebook
Note books are used during field work to record data obtained. The notebook should be of good quality and 150mm x100mm in size
A hard pencil and a rubber
Hard pencils are used for drawing in the field and a rubber is used to erase mistakes or errors which are made. A pencil should be HB or HHB.
Chain/Tape Surveying Activities at School Level
Practice chain/tape surveying activities at school level
Methods and procedures involved in chain survey
- A survey team involves three people, the leading chainman or leader, the follower and the booker.
- The chain is thrown to extend it and disentangle any knots
- The leader takes ten arrows and a ranging rod, and the follower takes a ranging rod The follower erects his ranging rod/pole at the first base point and places a brass handle of the chain against the ranging rod.
- A leader straightens the chain and inserts an arrow at end of the brass handle. Offsets and tie lines can now be taken.
- The leader drags the chain so that the follower‘s end is on the leader‘s arrow; the follower moves to another point and places his ranging pole behind the arrow. This procedure is then repeated.
The importance and usefulness of chain surveying
- It is suitable for small areas of fairly open ground.
- It is used to fill in details on a map whose large features have been surveyed by other methods.
- It is used in mapping small areas of flat or near-flat ground and associated objects, for example paths, roads and railways.
- It is used in adding detail to existing plans or large maps.
Advantages of chain surveying
- It is the simplest method of surveying through the old method.
- It is suitable for surveying clear areas.
- It tends not to attract attention.
- It is suitable for surveying a flat surface on the Earth‘s surface, for example a school compound.
- It can be read easily and quickly.
- It can withstand wear and tear.
- It can be easily repaired or rectified in the field.
Disadvantages of chain survey
- It is a slow method of surveying.
- It is the oldest method of surveying
- It is not suitable for surveying large areas.
- More difficult areas cannot be chain surveyed.
- Errors may be encountered due to the use of many chains and other reasons.
- It is time consuming.
- They are heavy and take too much time to open or fold.
- They become longer or shorter due to continuous use.
- When the measurement is taken in suspension, the chain sags excessively.
The Importance of Survey
Explain the importance of survey
Importance of surveying
- It help to prepare a topographical map which shows the hills, valleys, rivers, villages, towns, forests, etc. of a country.
- It helps to prepare a cadastral map showing the boundaries of the fields, houses and other properties.
- It help to prepare an engineering map which shows the details of engineering works such as roads, railways, reservoirs, irrigation canals, etc.
- It help to prepare a military map showing the road and railway communications with different parts of a country.
- It helps to prepare a contour map to determine the capacity of a reservoir and to find the best possible route for roads, railways, etc.
- It helps to prepare a geological map showing areas including underground resources.
- It helps to prepare an archaeological map including places ancient relics exist.
