Theory question 202
Surveying(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 a Chain Survey.
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(a) Ranging poles: straight wooden or metal poles about 2-3 m long, painted in red and white bands, pointed iron shoe; used to mark stations and line up survey lines.
Chain: 20 m or 30 m of steel links joined by rings, brass handles at both ends, tallies every few metres; used to measure distances.
Cross staff: a wooden head or metal box with slits at right angles, on a pole; used to set out offsets at right angles to the chain line.
Arrows: thin steel pins about 40 cm long with a pointed end and a ring at the top, usually 10 in a set; used to mark chain lengths and count them.
(b) Reconnaissance: walk over the area and choose stations; draw a rough sketch; fix stations with ranging poles so that they form triangles; measure each chain line (leader and follower, arrows counted); take offsets to features from the chain line with tape and cross staff; record everything in a field book; check lines; plot the survey to scale in the office.
Describe at least three instruments: what each looks like and what it is used for.