Excluding the climate, there's also many other factors such as:
1) Natural Resources - Water supply, food, fuel, building materials, ores, etc. are extremely important for survival
2) Natural disasters - Nobody would want to live right next to the volcano when there was much more other land in the past, they would certainly move away if natural disasters often occurred.
3) Transportation - People always settle near a river when they have a choice because it's more convenient to transport by boats. This can also help increase trades and greatly assist the city's economy.
