bibentry(
  bibtype = "article",
  author = "David Kahle and Hadley Wickham",
  title = "ggmap: Spatial Visualization with ggplot2",
  journal = "The R Journal",
  year = "2013",
  volume = "5",
  number = "1",
  pages = "144--161",
  url = "https://journal.r-project.org/archive/2013-1/kahle-wickham.pdf",
  textVersion = "D. Kahle and H. Wickham. ggmap: Spatial Visualization with ggplot2. The R Journal, 5(1), 144-161. URL http://journal.r-project.org/archive/2013-1/kahle-wickham.pdf"
)
