The study of physical and human landscapes, the processes that affect them, how and why they change over time, and how and why they vary spatially. Geographers determine the factors that influence landscapes or landscape features and seek to explain the interactions among them. This often involves explaining landscapes or environments from a spatial perspective by analyzing patterns or the lack of patterns. Geographers are also interested in the spatial arrangements of natural and human phenomena, as well as the relationships among these phenomena. Consequently, a key element of geography is areal differentiation, the process of defining regions with common unifying characteristics.