What aspect does a height map control in a 3D model?

A height map is a grayscale image used in 3D modeling that represents the physical height variations of a surface. Each pixel's brightness level corresponds to the elevation of that particular point on the terrain or object, where darker areas represent lower elevations and brighter areas represent higher elevations. By utilizing a height map, you can effectively create more realistic and complex surfaces, such as mountains, valleys, and other topographical features.

This method allows for the simulation of intricate details on 3D models without the need for an excessively high polygon count, enabling developers to maintain performance while achieving realistic terrain. In essence, height maps add depth and dimension to surfaces by controlling how high or low different parts of that surface are in relation to one another.