Installation art can be broadly defined as work which is three-dimensional and is produced in order to transform the perception of a space. In the past, this term was primarily meant to describe the hanging of pictures and other objects within an exhibition; in more recent times the term has come to signify work which deals directly with the space, the artist often creating mixed media assemblages designed for a temporary period of time. Site-specific work is closely related to Installation art in the sense that it is usually composed of objects installed at a location. Where the two may differ is that in a site specific work the artist is often dealing with the history, folklore, geography or social issues of a particular place; and in that sense the work can only exist at that location. In addition, because the work relies on being placed so specifically, many site-specific works are located outside of the gallery in, often unconventional, public spaces.