Defining the topography of a planetary body

River and landscape topography, combined, can reveal the geologic history of a planet Rivers develop on planetary bodies from the interplay of climate and topography. In planetary contexts, rivers and their effects are used to constrain short- and long-term climate models. However, rivers are also controlled by the short- and long-wavelength topography of the planetary surface. Rivers thus provide a means to constrain the generation of topography. On page 727 of this issue, Black et al. ( 1 ) compare topography at a range of scales with mapped river drainages to provide new insights into the topography-generating mechanisms on Earth, Mars, and Titan.