It is critical to understand the characteristics of public transportation networks (PTNs). Existing studies have mainly focused on the topological structure of PTNs and have revealed the commonalities of the topological structures of PTNs. However, few studies have examined the differences regarding topological structure characteristics between the PTNs of different cities. In addition, the nature and extent of the influence of specific urban geographic conditions and morphology on PTNs are unclear. This paper focuses on the influence of urban spatial and geographic environments on bus transportation networks (BTNs) by comparatively studying the topological and spatial attributes of two typical BTNs, respectively, from a mountainous city and a plain city in China, from the perspectives of basic statistical properties, types, connection properties, and spatial attributes, by using the complex networks theory and spatial analysis method. The results reveal that the two BTNs have similar statistical properties and they both have scale-free features as well as small-world features. However, these two BTNs are significantly different in the connection properties and spatial attributes. The difference is found closely related to the city’s geographic conditions and spatial morphology. The implications of this study regarding urban traffic planning and land planning are discussed.