Kahle and Wickham 2013

Kahle, David and Wickham, Hadley. 2013. ggmap: Spatial Visualization with ggplot2. The R Journal 5(1). 144–161.

@article{audersetinterrog-kahleggmap2013,
  author  = {Kahle, David and Wickham, Hadley},
  journal = {The R Journal},
  pages   = {144–161},
  title   = {ggmap: Spatial Visualization with ggplot2},
  volume  = {5(1)},
  year    = {2013}
}