Because of its unsanctioned element and its wide variations, the legitimacy of graffiti as an art form is constantly questioned. According to Bowen, the practice of graffiti first emerged as a phenomena called tagging. Tagging consists of different artists contriving ways of marking their initials or names in strongly stylized lettering and using these marks to denote places they either claimed as their territory or as a means of informing others that the territory had been infiltrated. Territorialism, as opposed to creativity and art, was the main motivation for the 1970s and 1980s New York graffiti artists. Their graffiti was considered vandalism, and was studied by sociologists, urban planners and anthropologists until placed in commercial galleries as art. As the taggers began to add more colors and images to their designs, graffiti became more advanced and started to cross the line between defacement and art. For many, therefore, it is considered the art of the streets. It was because of the easy accessibility to surfaces such as the subway cars in New York and the ability to gain widespread recognition throughout a large geographical area as these cars moved through the city that first gave rise to the art form in the 1970s. Through this medium, art was delivered throughout the boroughs. The unique position of graffiti enables it to become a voice of the common people. It is recognized as one of the strongest assertions of individual identity in the art world.