The word "横跨" is formed by combining the character "横", which conveys a sense of being horizontal or extending across, with the character "跨", which means to stride over or span. Together, they create a verb that specifically denotes the act of stretching or reaching across a physical or metaphorical space, such as a structure crossing from one point to another. The formation directly integrates the spatial orientation from "横" with the action from "跨" to express spanning across.