Hydrology is the study of the movement, distribution, and quality of water throughout Earth, and thus addresses both the hydrologic cycle and water resources. A practitioner of hydrology is a hydrologist, working within the fields of either earth or environmental science, physical geography, geology or civil and environmental engineering. Domains of hydrology include hydrometeorology, surface hydrology, hydrogeology, drainage basin management and water chemistry, where water plays the central role. Oceanography and meteorology are not included because water is only one of many important aspects. Hydrological research is useful as it allows us to better understand the world in which we live, and also provides insight for environmental engineering, policy and planning. The term ' is from Greek:, hydōr, "water"; and, logos, "study".