Cartography of very flat terrain: which method best represents subtle relief? For mapping a region with extremely low relief (near-flat topography), select the most effective technique for representing general topography on a plan.

Introduction / Context:
On nearly level terrain, the relief variations are subtle. If contour intervals are too large, many intermediate undulations will be missed and the map will appear deceptively flat. Choosing an appropriate contour interval is therefore central to faithful representation of the ground surface in topographic mapping.

Given Data / Assumptions:

• Terrain is very flat with small elevation differences.
• Goal is to depict general topography, not only isolated points.
• Standard planimetric accuracy and contouring practices apply.

Concept / Approach:

Contours connect points of equal elevation. The contour interval controls vertical resolution of the map. For flat lands, a small contour interval captures gentle rises and depressions. Conversely, a large interval would skip these variations. Spot levels are helpful supplements, but they cannot substitute for continuous depiction across the whole area when one seeks to visualize general relief patterns.

Step-by-Step Solution:

Verification / Alternative check:

Surveying standards recommend reducing the contour interval as the terrain becomes flatter; e.g., 0.2–0.5 m intervals are common for low-relief urban layouts.

Why Other Options Are Wrong:

Large interval (A) masks subtle relief.

Sparse spot levels (C) and only salient spots (D) do not portray continuous topography.

Hachures alone (E) are outdated and unsuitable for accurate quantitative elevation representation.

Common Pitfalls:

Keeping a uniform interval across very different terrains; failing to densify control to support small intervals.

Final Answer:

Drawing contours at a small interval