Reading the article and book and summarising them has highlighted key points and important information to do with graffiti and vandalism, however these sources are just two of many on the same subject. They may seem extremely believable as the facts and evidence are there but to guarantee that this is what should be believed and to expand my knowledge on the subject it would be advantageous to take my studies further.
To do so I would create a detailed list of there key points and conclusions to then find other books and articles on the same subjects. Using the library and the library cross search would allow me to do so and by reading a quick overview of the article on cross search I would decide if they were relevant.
At the end of "Urban Graffiti; Crime, Control and Resistance" there is a list of notes and references that relate to and give links to the evidence Ferrel has used to prove his points. To find out background information and grasp a better understanding of where he is coming from I would look up these references. He refers to a quote from Fiske (1991): "one has to look for the origins of evasion or resistance in the specific social circumstances of those who do this remaking." This quote is extremely important as it appears to be the inspiration to the whole introduction of the article so in this case I would take my studies further by looking up Fiske and find out he arrived at this conclusion.
"Design Against vandalism" lists all the materials and layouts that should be used to prevent vandalism so I would look up these suggested materials to find out how other people view there characteristics in connection with vandalism.
As the article and book were written quite a long time a go now I would research in to any newer books or articles by these authors on similar subjects. I could also look for reviews on the book and the article to see how other people have felt and see if they have suggested any other materials linked with the text.