Discrimination in the sale, renting and occupation of housing on the basis of race, colour, national or ethnic origin, leads to segregation in housing, ghettos and slums, and encourages racial conflict and division. Discrimination may be legalized (as in the South African system of apartheid where special areas are designated for Blacks or for Whites) or it may have evolved in practice (for example, at one time only 11% of privately-let property advertised in London did not specifically exclude coloured people). Discrimination may in the latter case take the form of refusal to rent, refusal to sell, or refusal to grant loans and mortgages. This may be based on the assumption that the person involved is not earning well, or the excuse may be along cultural lines, implying noise, gregariousness, dirty habits, etc, and the fact that this will reduce the value of the property in the vicinity.