Having built and assisted in a lot of cities, allow me to say that building terrain for a city is the hardest, most controversial parts. Should there be invisible walls or mountains? Should the grass be a yellowish-green, or a Lego green? If I make a lake, should I make it go straight down, or double the brick count and use slopes.
Balancing terrain with a city is hard. Wentworth's City RPG is my favorite example, and even then his mountain ranges shot straight up in spots. Nobody complained because the city itself had good content.