Which of the following describes a 3D model in geographic information science?

A 3D model in geographic information science is characterized by its ability to represent features with multiple z-values at each coordinate. This means that for each point defined by its x and y coordinates on the ground, the model can incorporate various elevations (z-values) to depict the terrain's vertical characteristics accurately. This capability is essential for representing complex landscapes, buildings, or geological formations where numerous layers of information can exist at the same horizontal location, such as in urban environments or layered geological deposits.

In contrast, the other options do not accurately reflect the nature of a 3D model. For instance, a model that allows only a single z-value for each coordinate confines to a simpler representation and does not fully capture the complexity of spatial relationships in three dimensions. A two-dimensional representation with elevation cues only offers a rudimentary sense of height without truly reflecting the three-dimensional space. A static map providing a top-down view typically presents only a flat layout, lacking the depth and elevation that a true 3D model encompasses. Thus, the correct choice highlights the complex and rich data representation that 3D models provide in geographic information science.