Theory question 202
Surveying(a) Explain the term error of closure. (b) Highlight any four sources of error of closure in closed traverse survey. (c) Outline two measures that could be taken to avoid an error of closure.
Show the model answer
(a) Error of closure is the gap between the starting point and the finishing point of a closed traverse when it is plotted, showing that the traverse fails to close exactly on its origin.
(b) Inaccurate measurement of lengths; wrong reading or booking of bearings; faulty or badly set instruments; local magnetic attraction (iron objects, power lines) deflecting the compass; errors in plotting (scale, protractor); sagging or stretched tape.
(c) Check and calibrate instruments before use; take forward and back bearings to check readings; measure each line twice; keep magnetic materials away from the compass; plot carefully and check booking.
Define the error, then list causes and the checks that prevent them.