Plane table surveying – naming the operation that makes all drawn lines parallel to ground directions The process of revolving the plane table about its vertical axis until every line on the drawing sheet becomes parallel to the corresponding line on the ground is called:

Introduction / Context:
Plane tabling is a rapid field-plotting method. Several preparatory operations are performed at each station: centering, levelling, and orientation. Many learners confuse these steps. This question focuses on the specific action of revolving the board so that all plotted lines are parallel to the corresponding ground directions, which is essential for direct graphical plotting.

Given Data / Assumptions:

• The plane table is already leveled in the sense of being made horizontal.
• The instrument is placed at a known station on the ground whose plotted position on the sheet is also known.
• The board can be rotated about its vertical axis until alignment is achieved.

Concept / Approach:

Levelling makes the board horizontal. Centering places the plotted station exactly over the ground station (usually by plumbing fork or optical plummet). Orientation is the action of rotating the board to make the directions of all plotted lines parallel to their actual directions on the ground, which can be done by backsighting a known point or by matching the magnetic meridian if magnetic orientation is used.

Step-by-Step Solution:

Verification / Alternative check:

If correctly oriented, rays plotted to multiple visible points should coincide with their ground directions; misorientation produces systematic parallel shifts in plotted detail.

Why Other Options Are Wrong:

Levelling: addresses horizontality, not directional parallelism.

Centering: locates the station position, not the directions.

Setting: a generic term sometimes used loosely, but not the precise technical term for this rotation step.

Common Pitfalls:

Attempting to begin detail plotting without verifying orientation; confusing magnetic orientation with backsight orientation; ignoring local attraction when using the magnetic method.

Final Answer:

Orientation