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Question 2
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(a) Describe any three of the following survey instruments:
(i) ranging poles;
(ii) chain;
(iii) cross staff;
(iv) arrows.
(b)
Outline the processes involved in carrying out chain survey. |
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This was an unpopular question among the candidates. Their performance on the (a ) part of the question was poor. Many of the candidates could not describe the survey instruments properly. Candidates should devote special attention to the segment on surveying since it is a vital aspects of the geography curriculum. Schools should purchase these instruments and put them to practical use. A description of each of the survey instrument is given below:
Ranging poles:
- made of light poles of circular section which is between 25 to 30 mm in diameter
- has iron shoe at one end to allow it to be fixed into the ground
- the poles are made of light metals or seasoned wood
- painted in alternate bright colours as white, red and black to make it visible from afar
- a ranging pole is between 1.8m – 3m in length
Chain:
- formed by 100 pieces of wire
- connected by small links
- there is brass handle for holding at the end of the chain
- the handle forms part of the distance
- the chain has 10 links
- the chain can be 66ft or 100ft; 20m or 30m long
- at every metre of the chain, there is a brass tag or tally to aid reading
- every 5m and 10m of the chain also carries a different tag for identification
Cross staff:
- made of metals
- the head is mounted on a shortened version of a ranging pole
- consist of cross with vertical end members
- each has slits
- the line of sight is between cross at right angles
- the arms are turned upwards at the ends
Arrows:
- thin painted steel wire
- has pointed metal markers
- about 381 mm or 15in long
- bent at the top into a ring
- to which red pieces of clothes can be attached to make them more visible
- painted in bright colours to make them easily visible
The processes involved in carry out chain surveying are:
- reconnaissance survey of the area
- sketch map
- chain survey requires a surveyor and two assistants
- surveyor stays at the starting point and a station is fixed
- a lead chainman is in front while the other holds the chain at the zero end.
- leader carries arrows and ranging poles
- with the poles, he aligns the points and moves the chain to line
- when the chain is steady at the zero point on a station A, the lead chainman fixes an arrow at the end of the chain length
- the leader then drags the chain towards the target station
- the distances measured are entered into the field notebook
- offsets are indicated
- The measured distances and offsets are plotted.
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