Theory question 202
Surveying(a) Describe, with the aid of a suitable diagram, an open traverse. (b) A compass traverse round a school compound produced the following field record:
Line AB: length 370 m, bearing 260°
Line BC: length 450 m, bearing 198°
Line CD: length 265 m, bearing 110°
Line DE: length 560 m, bearing 35°
Line EA: length 140 m, bearing 330°
Use the data above to: (i) plot the area of the compound on a scale of 1cm to 50m; (ii) find the direct distance between D and A, in metres.
Show the model answer
(a) An open traverse is a series of connected survey lines whose lengths and bearings are measured, starting at one point and ending at another without returning to the start (e.g. along a road or river). Diagram: a zig-zag line A-B-C-D-E with lengths and bearings marked, the end not joined to the start.
(b)(i) Convert lengths at 1 cm to 50 m: AB 7.4 cm, BC 9.0 cm, CD 5.3 cm, DE 11.2 cm, EA 2.8 cm; plot each line from the previous point on its bearing with a protractor from north lines; the traverse should close (almost) at A; give a title, scale and north arrow.
(ii) Measure DA on the plot (about 12.6-12.7 cm) and multiply by 50: about 630-635 m.
Convert each length to centimetres first, then plot bearings clockwise from north at each station.