(a) Describe any three of the following survey instruments: (i) ranging poles; (ii) chain; (iii) cross staff; (iv) arrows. (b) Outline the processes involve...

(a) Description of survey instruments (any three)

• (i) Ranging poles: straight wooden or metal poles about 2 to 3 metres long, painted in alternate bands of red and white (sometimes black) so that they are easily seen from a distance. They are pointed or shod with iron at the base to be stuck into the ground, and are used for marking survey stations and for ranging (keeping straight lines) during chaining.
• (ii) Chain: a measuring device made of a series of galvanised steel/iron links joined by rings, commonly the 20 m or 30 m chain, with brass tags/tallies at intervals to show the readings. It is used for measuring distances along the survey lines on fairly level ground.
• (iii) Cross staff: a small instrument (an octagonal box or frame with slits/sights, mounted on a pole) used to set out or measure right angles (offsets) from the chain line to features being surveyed.
• (iv) Arrows (chaining pins): pointed steel pins, usually a set of ten, with a ring at the top, used to mark the end of each chain length on the ground so that the number of chains measured can be counted.

(b) Processes involved in carrying out a Chain Survey

1. Reconnaissance: walk over and study the area to be surveyed to plan the survey lines and station positions.
2. Marking stations and drawing a key/index sketch of the framework of survey lines (well-conditioned triangles).
3. Ranging the main (base/chain) line using ranging poles to keep it straight.
4. Chaining the survey lines, measuring distances with the chain and inserting arrows at each chain length.
5. Taking offsets to features on either side of the chain line using the cross staff/tape, and booking all measurements neatly in the field book.
6. Applying check lines/tie lines to verify accuracy, then plotting the survey to scale in the office to produce the map.