Fundamentals of meridians in surveying and geodesy Which definition best describes the meridian of a place on the Earth, considering geographic (terrestrial) meridians used for mapping and navigation?

Introduction / Context:
Meridians are fundamental reference circles used in geography, geodesy, and surveying to define longitudes and directions. Choosing the correct definition clarifies how positions are referenced on maps and how celestial observations are related to Earth-fixed directions.

Given Data / Assumptions:

• We refer to terrestrial (geographic) meridians on the Earth’s surface.
• Meridians are used to define longitude and great-circle directions north–south.
• Terminology distinguishes between a full great circle (meridian) and its halves (individual “meridians” used in some celestial contexts).

Concept / Approach:
On a sphere, a meridian is the great circle that passes through the Earth’s rotation poles. Every location on Earth lies on a unique meridian. While some celestial-sphere definitions describe the local meridian as a semicircle through the zenith terminating at the poles, the terrestrial meridian in mapping is the entire great circle through both poles and the place.

Step-by-Step Solution:
Identify the Earth-based definition used in surveying and mapping.A meridian must pass through the place and both poles → great circle criterion.Hence option (a) matches the standard geographic definition most precisely.

Verification / Alternative check:
Longitude is measured along the equator from a prime meridian; each longitude corresponds to a specific great circle through both poles—confirming the great-circle definition.

Why Other Options Are Wrong:

• (b) A plane perpendicular to the rotation axis is the equatorial plane, not a meridian plane.
• (c) A semicircle describes only half of the great circle; while used in celestial context, the terrestrial definition is better stated as the full great circle.
• (d) “Perpendicular to the equator” is true for any meridian arc, but the wording as an “arc” is incomplete compared with the standard great-circle definition.

Common Pitfalls:
Confusing terrestrial meridians with the observer’s “local meridian” on the celestial sphere; the former is a full great circle on Earth, the latter is often described as a semicircle through the zenith.

Final Answer:
A great circle passing through the place and through both geographic poles