To cite package sp in publications use:

Pebesma EJ, Bivand RS (2005). “Classes and methods for spatial data in R.” R News, 5(2), 9–13. https://CRAN.R-project.org/doc/Rnews/.

Bivand RS, Pebesma E, Gomez-Rubio V (2013). Applied spatial data analysis with R, Second edition. Springer, NY. http://www.asdar-book.org/.

Corresponding BibTeX entries:

  @Article{,
    author = {Edzer J. Pebesma and Roger S. Bivand},
    title = {Classes and methods for spatial data in {R}},
    journal = {R News},
    year = {2005},
    volume = {5},
    number = {2},
    pages = {9--13},
    month = {November},
    url = {https://CRAN.R-project.org/doc/Rnews/},
  }
  @Book{,
    author = {Roger S. Bivand and Edzer Pebesma and Virgilio
      Gomez-Rubio},
    title = {Applied spatial data analysis with {R}, Second edition},
    year = {2013},
    publisher = {Springer, NY},
    url = {http://www.asdar-book.org/},
  }