To cite package sp in publications use:

Pebesma, E.J., R.S. Bivand, 2005. Classes and methods for spatial data in R. R News 5 (2), http://cran.r-project.org/doc/Rnews/.

Roger S. Bivand, Edzer Pebesma, Virgilio Gomez-Rubio, 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 = {http://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/},
  }