The Köppen climate classification system (Wladimir Köppen, 1884) divides Earth's climates into 5 main groups (A-E) and numerous subtypes. Group A (tropical): Af (rainforest), Am (monsoon), Aw (savanna). Group B (arid): BWh/BWk (desert), BSh/BSk (steppe). Group C (temperate): Cfb (oceanic), Cfa (humid subtropical), Csa/Csb (mediterranean). Group D (continental): Dfb (humid continental), Dfc (subarctic). FashionFactory maps all 57 cities to Köppen classes for climate-appropriate fabric recommendations.