Curve designation in surveying – standard definition used in practice By what is the designation of a (horizontal) curve commonly defined in classical surveying practice?

Introduction / Context:
Horizontal curves are often specified by their degree of curve in roadway and railway work. While curvature and radius are fundamental properties, field-friendly definitions are historically preferred. This question asks which definition is used for the designation in classical (particularly metric/Indian) practice.

Given Data / Assumptions:

• Degree of curve is a conventional measure related to radius.
• In many systems, the degree of curve is linked to a standard arc length (e.g., 30 m in metric practice).
• Alternative chord definitions are also used in some regions, but the question targets the classical arc-based definition.

Concept / Approach:

In the arc-based system, the degree of curve is the angle subtended at the center by an arc of specified standard length. This provides a direct and uniform relationship between degree and radius: larger degree corresponds to smaller radius. Although some manuals (notably in the U.S.) use the chord-based definition (angle subtended by a standard chord), the arc definition is the conventional one cited in many surveying syllabi and texts.

Step-by-Step Solution:

Verification / Alternative check:

Worked examples equate degree of curve and radius through the arc formula; tables list R for various D assuming the standard arc length.

Why Other Options Are Wrong:

Chord of any length: ambiguous; the standard uses a specified arc or chord length.

Radius: while fundamental, many field tables and instruments rely on degree rather than directly quoting radius.

Curvature: mathematically valid (1/R) but not the traditional designation in field notes.

Common Pitfalls:

Mixing arc-based and chord-based systems; forgetting to use the correct standard length when converting between D and R.

Final Answer:

Angle subtended by an arc of specified length