aspect

The direction a slope faces — and therefore the amount of sun, heat, and moisture it receives. A south-facing slope in the northern hemisphere gets hammered by sun; its north-facing neighbor stays cool and damp. The two sides of the same canyon can carry entirely different plant communities, hold snow for different durations, and feel like different climates. Aspect is the reason the world changes when you walk around a hill. The word is plain but the concept is foundational — you can't read a landscape without it.