water. Such settlements also exist in industrialized countries, such as for example Cañada Real on the outskirts of Madrid. Squatting can be related to political movements, such as anarchist, autonomist, or socialist. It can be a means to conserve buildings or a protest action. Squats can be used by local communities as free shops, cafés, venues, pirate radio stations or as multi-purpose autonomous social centres. Dutch sociologist Hans Pruijt separates types of squatters into five distinct categories: Deprivation-based – homeless people squatting for housing need An alternative housing strategy – people unprepared to wait on municipal lists to be housed take direct action Entrepreneurial – people breaking into buildings to service the need of a community for cheap bars, clubs etc. Conservational – preserving monuments because the authorities have let them decay Political – activists squatting buildings as protests or to make social centres Adverse possession, sometimes described as squatter's rights, is a method of acquiring title to property through possession for a statutory period under certain conditions. Countries where this principle exists include England and the United States, based on common law. Anarchist author Colin Ward asserts: "Squatting is the oldest mode of tenure in the world, and we are all descended from squatters. This is as true of the Queen [of the United Kingdom] with her as it is of the 54 percent of householders in Britain who are owner-occupiers. They are all the ultimate recipients of stolen land, for to regard our planet as a commodity offends every conceivable principle of natural rights." Others have a different view; UK police official Sue Williams, for example, has stated that "Squatting is linked to anti-social behaviour and can cause a great deal of nuisance and distress to local residents. In some cases there may also be criminal activities involved." The public attitude toward squatting varies, depending on legal aspects, socioeconomic conditions, and the type of housing occupied by squatters. In particular, while squatting of municipal buildings may be treated leniently, squatting of private property can often lead to strongly negative reactions on the part of the general public and the authorities. Africa In African countries such as Nigeria, informal settlements are created by migration from rural areas to urban areas. Reasons for squatting include the lack of low cost housing, unemployment and inability to access loans. In 1995, almost 70% of the population of the Nigerian capital Lagos were