To cite the micromap package in publications use:

  Quinn C. Payton, Michael G. McManus, Marc H. Weber, Anthony R. Olsen,
  and Thomas M. Kincaid (2015). micromap: A Package for Linked
  Micromaps. Journal of Statistical Software, 63(2), 1-16. URL
  https://www.jstatsoft.org/v63/i02/.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{micromap}: A Package for Linked Micromaps},
    author = {Quinn Payton and Tony Olsen and Marc Weber and Michael McManus and Tom Kincaid and Marcus W. Beck},
    journal = {Journal of Statistical Software},
    year = {2015},
    volume = {63},
    number = {2},
    pages = {1--16},
    doi = {10.18637/jss.v063.i02},
  }