(a) Describe, with the aid of a… | Geography

Question 1 Report

(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	Length (mm)	Bearing
AB	370	260º
BC	450	198°
CD	265	110°
DE	560	35°
EA	140	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.

Answer

(a) Open traverse

An open traverse is a series of connected survey lines whose lengths and bearings are measured, beginning at one station and ending at another station. It does not return to, or close at, the starting point. It is suitable for surveying linear features such as roads, railway lines, rivers and pipelines.

An open traverse starts at A and ends at E without closing at the starting station.

(b) Compass traverse of the school compound

The given field lengths are taken as metres. At a scale of 1 cm to 50 m, the representative fraction is:

\[1:5\,000\]

Line	Ground length (m)	Bearing	Length on plan (cm)
AB	370	260°	7.4
BC	450	198°	9.0
CD	265	110°	5.3
DE	560	35°	11.2
EA	140	330°	2.8

(i) Plot of the compound

Using a protractor, set off each bearing clockwise from north at the appropriate station and draw the corresponding scaled length. The completed traverse is shown below.

Compass traverse plotted from the given bearings and scaled lengths. The broken line DA measures about 12.7 cm.

(ii) Direct distance DA

From the plotted plan, the straight-line distance from D to A measures approximately \(12.7\text{ cm}\).

\[DA=12.7\times 50\text{ m}=635\text{ m}\]

Therefore, the direct distance between D and A is approximately 635 m.

Check by computation from the first three traverse lines:

Line	Easting, \(L\sin\theta\) (m)	Northing, \(L\cos\theta\) (m)
AB	\(-364.4\)	\(-64.2\)
BC	\(-139.1\)	\(-428.0\)
CD	\(+249.0\)	\(-90.6\)
D relative to A	\(-254.5\)	\(-582.8\)

\[DA=\sqrt{(254.5)^2+(582.8)^2}\approx636\text{ m}\]

This agrees with the scaled answer of 635 m, allowing for plotting and measurement.

Read lesson note on Field Work (WAEC)

Read lesson note on Principles Of Elementary Surveying* (WAEC)

Answer Details