A pattern of contour lines forms a V when crossing a stream valley. The point of the V indicates upstream, while the opening of the V indicates downstream.
Once a V pattern is found, the stream valley and boundaries of the watershed can be traced by looking at the distance between contour lines. This distance represents the slope of the land. As land begins to slope, contour lines are drawn closer together. Contour lines that are very close together represent a steeper slope than those that are farther apart. Contour lines that are far apart represent fairly level land. They indicate the boundary of the watershed with water flowing down slopes moving away from the boundary.