A reference plane (folding plane) that separates two related views appears edge-on (as a line) in the adjacent view. Is this descriptive-geometry statement correct?

Introduction / Context:
In multiview projection, each view is related to its neighbor across a folding or reference plane. Because we look perpendicular to a view’s plane, the folding plane itself is seen edge-on in the adjacent view, which is why it is drawn as a single line (the reference line). We assess this claim for correctness.

Given Data / Assumptions:

• Two adjacent views share a folding plane.
• Observer looks normal to the projection plane.
• Edge-on viewing collapses a plane to a line in projection.

Concept / Approach:
A plane projects to a line when it is perpendicular to the line of sight (i.e., observed edge-on). The adjacent view is arranged so that its folding plane is indeed edge-on, hence represented by a single straight line which we call the reference line (e.g., X–Y line in first-angle/third-angle conventions).

Step-by-Step Solution:
1) Identify the pair of adjacent views (e.g., front and an auxiliary).2) Establish the folding plane between them.3) Recognize that the folding plane is seen edge-on from either view, so it collapses to a line.4) Use this line as the locus for perpendicular projectors to transfer geometry.

Verification / Alternative check:
Constructing a simple box and adjacent view shows the folding plane as a shared line; any attempt to draw it as an area would contradict orthographic theory.

Why Other Options Are Wrong:
Rectangle/arbitrary appearance: A plane appears as an area only when not edge-on; here it must be edge-on.“Incorrect”: Denies a fundamental projection property.

Common Pitfalls:
Confusing the physical paper margin with the geometric reference line; misplacing the reference line so projectors are no longer perpendicular.

Final Answer:
Correct