To cite tmap/tmaptools in publications use:

  Tennekes M (2018). “tmap: Thematic Maps in R.” _Journal of
  Statistical Software_, *84*(6), 1-39. doi:10.18637/jss.v084.i06
  <https://doi.org/10.18637/jss.v084.i06>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {{tmap}: Thematic Maps in {R}},
    author = {Martijn Tennekes},
    journal = {Journal of Statistical Software},
    year = {2018},
    volume = {84},
    number = {6},
    pages = {1--39},
    doi = {10.18637/jss.v084.i06},
  }