Complex sentence: An Aesthetic Study of Graffiti on the Subway System of New York City, 1970-1978, U.M.I., Ann Arbor, MI, 1989, is the only known study of NYC subway graffiti that was investigated almost entirely from primary sources.
Split into simpler sentences: An Aesthetic Study of Graffiti on the Subway System of New York City, 1970-1978, U.M.I., Ann Arbor, MI, 1989. This is the only known study of NYC subway graffiti that was investigated almost entirely from primary sources.