The general visual style of modern graffiti evolved from the confluence of sociological and material elements. The sociological element is that of young people, originally of under-class demographics but now extending beyond class barriers, who want to leave a public signature (a tag), but quickly, so as not to get caught. The material element is the spray can. The reason that writers use spray cans for anything beyond a small tag (markers work well for those), is that the spray can, easily concealable and portable, can cover a large area quickly yet with control. And even though now there are legal forums for public art, where spray painting may be done in a relaxed manner, the stylish and often spontaneous look of the finished product comes from the roots of this movement. Something that stands out in the best work is the authority of technique and “pulp” energy that results from often having time limits and the knowledge that the work being done is illegal and will probably be gone in short order. A central goal in graffiti is the development of a distinctive visual style, same as it is for most any artist. The development of this individual style is the single determining factor in how a writer is judged among his peers, the ultimate audience to impress. Various writers may be known for other attributes such as can control or color palette, but without an inspired creative letter style, a writer will never be considered in the top tier. Just look up at the billboards and buildings around you to appreciate this other kind of high art. More about this interesting article in AIGA, here.