To cite rpostgis in publications use:

  Bucklin, D. & Basille, M. (2018). rpostgis: linking R with a PostGIS
  spatial database. The R Journal, 10(1), 251-268.
  https://journal.r-project.org/archive/2018/RJ-2018-025/index.html

A BibTeX entry for LaTeX users is

  @Article{,
    title = {rpostgis: linking R with a PostGIS spatial database},
    author = {David Bucklin and Mathieu Basille},
    journal = {The R Journal},
    volume = {10},
    number = {1},
    pages = {251-268},
    year = {2018},
    url = {https://journal.r-project.org/archive/2018/RJ-2018-025/index.html},
  }