Geographers are particularly interested in systems that link together human beings and environment. Figure 1.11 shows such a system , linking the users of a particular beach with its environment. Here a human system, and an environmental system are linked into a human-environment system . the link are of various kinds-information, energy, and material. Together they form the flows that bind the five elements together. Note in particular the circular loop connecting the character of the beach and the density of those using it . Higher levels of use may lead to two effects: first, to growing litter and pollution ,which may lead people to shun the beach and move elsewhere. Since this effect lessens the use of the beach , this kind of feedback is termed a negative feedback. A second and opposite effect may be for more people to increase the attractiveness of the beach. For example, on a popular beach it may be worthwhile to provide a lifeguard. This second effect is termed a positive feedback, since it tends to increase the level of use.