The best pyramid for this is the biomass pyramid. That is because they show how much ecological material can be found at each trophic level, which then can be used to model how the matter flows through the ecosystem that is being analyzed.
People, Goods, and Ideas are what mostly Geographers talk about.
The main reason for the wall's construction had always been defense. Since China's first dynasty, the empire faced a near-constant threat of attack from the nomadic tribes to the north. This included those famed Mongols as well as lesser-known groups like the Xiongnu and the Göktürks.
The movement of groups from one country,place, or locality to another
