Line on the Earth’s surface with constant slope: precise terminology An imaginary line traced over the ground that everywhere maintains a constant inclination to the horizontal plane is called:

Introduction / Context:
Several kinds of lines are used in surveying and mapping, and their names are sometimes confused. A contour line connects points of equal elevation (zero slope relative to the horizontal). In contrast, a route designer often needs a line that rises or falls steadily at a specified slope. This question checks the proper term for such a constant-slope path on the ground surface.

Given Data / Assumptions:

• The line lies on the topographic surface (not a straight line in 3D space).
• The inclination to the horizontal is fixed at every point (constant gradient).
• Standard civil engineering terminology is used.

Concept / Approach:

The correct term is “contour gradient”: a line on the ground that has a uniform slope with respect to the horizontal. It is commonly used in alignment design for roads, canals, and pipelines to maintain drainage or energy grade. A level line is a locus of points of equal elevation (zero slope). A “line of gentle slope” is merely descriptive and not a precise technical term.

Step-by-Step Solution:

Verification / Alternative check:

Textbooks on surveying and highway engineering define a contour gradient as a line with a specified slope laid on the map by proportional rise or fall between contours.

Why Other Options Are Wrong:

Contour line: constant elevation rather than constant slope.

Level line: a curve everywhere normal to gravity; again, zero slope relative to horizontal.

Line of gentle slope: not a standard term and does not imply constancy.

Common Pitfalls:

Confusing “contour” with “contour gradient”; assuming any sloping line suffices without verifying constant inclination.

Final Answer:

Contour gradient