Geography is the study of the Earth and its features. It comes from the Greek words "geo" meaning Earth and "graphein" meaning to write or describe. Geography literally means to write about the Earth. Maps and globes are tools used to represent and model Earth's physical features, landmasses, bodies of water, and political boundaries. Early civilizations developed along river valleys such as the Tigris-Euphrates, Indus, Huang He, and Nile Rivers.