Which technique is often utilized for relief representation in 2D maps?

Relief representation in 2D maps is essential for conveying the three-dimensional features of the Earth's surface, and several techniques can effectively illustrate this.

Shading is a technique that utilizes the play of light and shadow to create an illusion of depth on flat maps, enhancing the perception of terrain variations. It simulates the way light interacts with the landscape, helping viewers visualize hills and valleys.

Color gradients are employed to represent elevation changes by using a spectrum of colors, where different colors correspond to different elevations. This method can effectively communicate variations in terrain by allowing users to quickly ascertain height differences visually.

Contour intervals are lines drawn on a map to connect points of equal elevation, and they provide a clear and standardized means of understanding the shape of the terrain. By indicating where the land rises and falls, contour lines help users grasp the topography's intricacies.

Each of these techniques contributes to effective relief representation, and thus, stating "all of the above" acknowledges the utility of a comprehensive approach combining shading, color gradients, and contour intervals for a better understanding of geographical features. This multifaceted technique allows cartographers to cater to various needs and preferences in map interpretation.