Spatial analysis of graffiti in San Francisco

• Commercial zones have the highest rate of graffiti reports in San Francisco.
• Graffiti is created in areas with high densities of young males.
• GWR model is consistent with graffiti as communication, and with the broken window theory.
• GWR model explains over two-thirds of the variation in S.F. graffiti reports.
• GWR explains graffiti report variation better than OLS does.

Graffiti, as a social phenomenon, has been with us since people first began painting on cave walls. Our responses to graffiti range from recognition of artistry, to interpreting it as a sign of urban decay and disorder. Major cities respond to tax-payers with this latter response by providing graffiti abatement programs, often at substantial cost; thus, understanding and mitigating the causes of graffiti has tangible value. Using spatial analysis, we explore the combined causes of graffiti creation and the subsequent reporting of graffiti for removal in San Francisco, CA, USA. Using a combination of census data and city data, we identify five factors that have significant correlation to graffiti reports, and use them to build a regression model. We show that graffiti is created in areas with high densities of young males, and that commercial zones have the highest rate of graffiti reports. We show that a Geographically Weighted Regression model of these five factors explains over two-thirds of the variation in graffiti reports in San Francisco. Further, our findings are consistent with the dual hypotheses of graffiti as a form of communication or advertising aimed at a target market of other young males, along with the broken window thesis of graffiti interpreted as a sign of social disorder.

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