The inner city is the central area of a major city or metropolis and may also refer to the Urban Land Use Model. In the United States, the term is often a euphemism applied to the lower-income residential districts in the city centre and nearby areas. In the United States, the term has the additional connotation of impoverished black and/or Hispanic neighborhoods. Sociologists sometimes turn this euphemism into a formal designation, applying the term inner city to such residential areas rather than to geographically more central commercial districts.[citation needed]However, some inner city areas of American cities have undergone gentrification especially since the 1990s.[1]Such connotations are less common in other countries, where deprived areas may be located in outlying parts of cities. For instance, in many European cities, the inner city is the most prosperous part of the metropolis, where housing is expensive and where elites and high-income individuals dwell. Poverty and crime are more associated with the distant suburbs. The Italian, Spanish, Portuguese, French and Swedish words for suburb (sobborgo, suburbio, subrbio, banlieue and frort respectively) often have a negative connotation similar to that of the English term inner city, especially when used in the plural.The American sociological usage is rooted in the middle 20th century. When automobiles became affordable in the United States and forced busing ensued, many middle and high-income residents, who were mostly white, moved to suburbs to have larger lots and houses, and a lower crime rate. The loss of population and affluent taxpayers caused many inner city communities to fall into urban decay. Late in the century, many such areas underwent gentrification, especially in the Northeast and West coast, depriving them of the "inner city" label despite their unchanged location.Regardless of their degree of prosperity, city areas that are literally more central tend to have higher population densities than outer suburbs, with more of the population living inside multi-floored townhouses and apartment buildings.