Here's why:

* Thickly Clouded: Venus has a dense atmosphere composed primarily of carbon dioxide, resulting in thick, opaque clouds that obscure the surface from direct visual observation.

* Radar Mapping: Due to the thick clouds, radar mapping has been crucial in revealing the surface features of Venus.

* Varied Topography: Radar data has revealed a varied topography on Venus, including vast plains, elevated highlands, and numerous volcanic structures.

Let me know if you'd like to know more about Venus!