It is an area that feeds all the water running under it and draining off of it into a body of water. It may integrate other watersheds to form a network of rivers and streams and progressively drain into larger water areas. Topography determines where and how water flows. Ridge tops surrounding a body of water determine the boundary of a watershed. Watershed can be categorised into symmetrical and asymmetric forms. The dividing line of a symmetrical watershed is located at the centre of the watershed, and the slope gradients and lengths on both sides are identical. The dividing line of an asymmetrical watershed is skewed towards one side, and the two slopes are not symmetrical. Symmetrical watersheds are very rare, and most watersheds are asymmetrical.