What feature, appearing on a map as a U or V shape, represents a small valley?

The feature that appears on a map as a U or V shape and represents a small valley is known as a re-entrant. Re-entrants are typically formed by the process of erosion, which creates a channel down the side of a hill or mountain. In topographic maps, the contour lines illustrate elevation; when they form a U or V shape, it indicates a downward slope into a lower area, characteristic of a valley.

Understanding how re-entrants are represented on a map is crucial for navigational purposes and terrain analysis. They can influence various factors such as water flow, vegetation patterns, and potential routes for movement within that landscape. On the other hand, contour lines represent the elevation and shape of the terrain without specifically denoting valleys, while sinkholes are depressions or holes that occur when the ground collapses, and gullies are steeper channels created by surface runoff, neither of which correspond to the U or V shape characteristic of a re-entrant.