Contouring Method Selection – Best Technique for Undulating Terrain For preparing contours over an undulating area (moderate relief with frequent rises and falls), which field method is generally preferred for efficiency and accuracy?

Introduction / Context:
Contouring requires rapid determination of many spot levels across varying ground. The chosen method must efficiently capture both plan position and elevation. This question asks which classical technique is most suitable on undulating ground when speed and reasonable accuracy are needed.

Given Data / Assumptions:

• Undulating (not mountainous) terrain with frequent gentle slopes.
• Need for numerous points to interpolate smooth contour lines.
• Conventional, non-EDM/total-station classical methods.

Concept / Approach:

Tacheometry simultaneously provides horizontal distance and elevation differences from a single instrument setup using stadia or tangential methods. This dual capture makes it ideal for contouring over variable ground. Chain or compass alone lack elevation capability. Plane table is excellent for plan detail but needs levelling add-ons; pure plane table methods are slower for dense heighting unless combined with tacheometry (alidade with stadia hairs).

Step-by-Step Solution:

Verification / Alternative check:

Classical surveying texts recommend tacheometry for contouring undulating areas; modern practice uses total stations which are an evolution of the same principle.

Why Other Options Are Wrong:

Chain/compass give plan but not heights; plane table alone is slower for heights; barometric levelling is too crude for detailed contour maps.

Common Pitfalls:

Under-sampling elevations; ignoring closed-loop checks for control points; not accounting for steep pockets where closer spacing is required.

Final Answer:

Tacheometrical surveying