What does a deflection angle measure in surveying?

• A. The angle between two parallel lines
• B. The angular deviation from the back survey line to the forward line
• C. The total change in angle during a survey
• D. The angle of elevation of terrain

Answer: (B)

A deflection angle in surveying specifically measures the angular deviation from a back survey line to a forward survey line. This is critical in the process of laying out or aligning new survey lines, as it helps in determining how much the direction of the line changes from a previous reference point.

In practical terms, when conducting a survey, a land surveyor often needs to switch from surveying in one direction (the back line) to the next (the forward line) to accurately map out the area. The deflection angle indicates how much the line has turned from the direction of the previous survey line.

This concept is particularly important in the fields of civil engineering and construction, where precise angular measurements directly affect the placement of structures and ensure that they are oriented correctly within the planned design.