Topographic interpretation — closed contour lines whose elevations decrease towards the centre indicate which landform?

Introduction / Context:
Reading contour maps is foundational for site selection, alignment design, drainage planning, and hazard assessment. The pattern and sequencing of contour values convey landform types such as hills, valleys, depressions, and saddles. This question tests recognition of a classic pattern: decreasing contour values toward a closed centre.

Given Data / Assumptions:

• Contours are closed and labelled with elevation values.
• There are no form lines or supplementary features overriding interpretation.
• Standard cartographic conventions are used.

Concept / Approach:

Closed contours where elevation values decrease towards the centre represent a topographic depression (basin, sink). The opposite pattern—values increasing towards the centre—marks a hill. A saddle shows two opposing highs connected by a low pass, producing hourglass-shaped contours. A river bed is indicated by V-shaped contours pointing upstream, not by concentric decreases unless the river occupies a closed basin.

Step-by-Step Solution:

Verification / Alternative check:

Standard mapping references adopt this interpretation; many maps add short ticks on depression contours pointing downslope to avoid ambiguity.

Why Other Options Are Wrong:

Hill — requires increasing values inward.
Saddle — needs two ridges separated by a pass, not nested decreasing loops.
River bed — generally open V shapes pointing upstream, not closed loops.

Common Pitfalls:

Misreading the sign of elevation change; overlooking closed contour hachures; confusing depression with crater versus sinkhole—both are depressions by contour logic.

Final Answer:

a depression