I think I understand what Chris is saying. I believe the reason we do not see many Sci-Fi city vistas with hills and mountains is that the implication is made that the works of humankind (or alienkind) have surpassed the very works of nature as far as scale or vastness. Mountains and canyons still dwarf by comparison the greatest structures and buildings that humankind has made thus far into the early 21st century. What better way to show that a advanced civilization can control the entire resources and energy output of a planet, solar system, or even galaxy than to show that nature itself has been conquered. Thus there are no majestic mountains or valleys to conflict visually with the tremendously vast scale of the Sci-fi "dystopian" mega-city. Or, they might be great at building models and piss-poor at making landscapes!